Advertisement

Maternal and neonatal outcomes in electively induced low-risk term pregnancies

Published:March 13, 2014DOI:https://doi.org/10.1016/j.ajog.2014.03.016

      Objective

      Elective induction of labor has been discouraged over concerns regarding increased complications. We evaluated the mode of delivery and maternal and neonatal morbidities in low-risk patients whose labor was electively induced or expectantly managed at term.

      Study Design

      This was a retrospective cross-sectional study from 12 US institutions (19 hospitals), 2002 through 2008 (Safe Labor Consortium). Healthy women with viable, vertex singleton pregnancies at 37-41 weeks of gestation were included. Women electively induced in each week were compared with women managed expectantly. The primary outcome was mode of delivery.

      Results

      Of 131,243 low-risk deliveries, 13,242 (10.1%) were electively induced. The risk of cesarean delivery was lower at each week of gestation with elective induction vs expectant management regardless of parity and modified Bishop score (for unfavorable nulliparous patients at: 37 weeks = 18.6% vs 34.2%, adjusted odds ratio, 0.40; [95% confidence interval, 0.18–0.88]; 38 weeks = 28.4% vs 35.4%, 0.65 [0.49–0.85]; 39 weeks = 23.6% vs 38.5%, 0.47 [0.38–0.57]; 40 weeks = 32.3% vs 42.3%, 0.70 [0.59–0.81]). Maternal infections were significantly lower with elective inductions. Major, minor, and respiratory neonatal morbidity composites were lower with elective inductions at ≥38 weeks (for nulliparous patients at: 38 weeks = adjusted odds ratio, 0.43; [95% confidence interval, 0.26–0.72]; 39 weeks = 0.75 [0.61–0.92]; 40 weeks = 0.65 [0.54–0.80]).

      Conclusion

      Elective induction of labor at term is associated with decreased risks of cesarean delivery and other maternal and neonatal morbidities compared with expectant management regardless of parity or cervical status on admission.

      Key words

      Conventional obstetric teaching, based on early studies of induction of labor, suggested that an elective induction of labor is associated with increased maternal morbidities such as cesarean section, length of labor, and infection.
      • Yeast J.D.
      • Jones A.
      • Poskin M.
      Induction of labor and the relationship to cesarean delivery: a review of 7001 consecutive inductions.
      • Smith K.M.
      • Hoffman M.K.
      • Sciscione A.
      Elective induction of labor in nulliparous women increases the risk of cesarean delivery.
      • Hoffman M.K.
      • Vahratian A.
      • Sciscione A.C.
      • Troendle J.F.
      • Zhang J.
      Comparison of labor progression between induced and noninduced multiparous women.
      However, publications supporting this teaching compared induction of labor with spontaneous labor,
      • Glantz J.C.
      Elective induction vs spontaneous labor: associations and outcomes.
      rather than the true clinical alternative of expectant management.
      • Caughey A.B.
      • Nicholson J.M.
      • Cheng Y.W.
      • Lyell D.J.
      • Washington A.E.
      Induction of labor and cesarean delivery by gestational age.
      Several studies have presented information refuting the association of induction with increased cesarean delivery.

      The National Institute of Child Health and Human Development Network of Maternal-Fetal Medicine Units. A clinical trial of induction of labor versus expectant management in postterm pregnancy. Am J Obstet Gynecol 1994;170:716-23.

      • Cole R.A.
      • Howie P.W.
      • Macnaughton M.C.
      Elective induction of labor: randomized prospective trial.
      • Hannah M.E.
      • Hannah W.J.
      • Hellmann J.
      • Hewson S.
      • Milner R.
      • Willan A.
      Induction of labor as compared with serial antenatal monitoring in post-term pregnancy: a randomized controlled trial; the Canadian Multicenter Post-term Pregnancy Trial Group.
      • Caughey A.B.
      • Sundaram V.
      • Kaimal A.J.
      • et al.
      Systematic review: elective induction of labor versus expectant management of pregnancy.
      Two large prospective multicenter studies of late term (41 weeks' gestational age) pregnancies found no difference

      The National Institute of Child Health and Human Development Network of Maternal-Fetal Medicine Units. A clinical trial of induction of labor versus expectant management in postterm pregnancy. Am J Obstet Gynecol 1994;170:716-23.

      • Cole R.A.
      • Howie P.W.
      • Macnaughton M.C.
      Elective induction of labor: randomized prospective trial.
      or a decreased rate of cesarean delivery
      • Hannah M.E.
      • Hannah W.J.
      • Hellmann J.
      • Hewson S.
      • Milner R.
      • Willan A.
      Induction of labor as compared with serial antenatal monitoring in post-term pregnancy: a randomized controlled trial; the Canadian Multicenter Post-term Pregnancy Trial Group.
      in elective inductions vs expectant management. A metaanalysis reported an absolute risk reduction in cesarean delivery rate with elective induction of 1.9% (95% confidence interval [CI], 0.2–3.7%) for late term and postterm pregnancies.
      • Caughey A.B.
      • Sundaram V.
      • Kaimal A.J.
      • et al.
      Systematic review: elective induction of labor versus expectant management of pregnancy.
      Similar findings have been reported across different obstetric cohorts, including those with hypertensive disease,
      • Koopmans C.M.
      • Bijlenga D.
      • Groen H.
      • et al.
      HYPITAT Study Group
      Induction of labor versus expectant monitoring for gestational hypertension or mild pre-eclampsia after 36 weeks' gestation (HYPITAT): a multicenter, open-label randomized controlled trial.
      fetal growth restriction,
      • Boers K.E.
      • Vijgen S.M.
      • Bijlenga D.
      • et al.
      DIGITAT Study Group
      Induction versus expectant monitoring for intrauterine growth restriction at term: randomized equivalence trial (DIGITAT).
      and diabetes.
      • Kjos S.L.
      • Henry O.A.
      • Montoro M.
      Insulin-requiring diabetes in pregnancy: a randomized trial of active induction of labor and expectant management.
      • Rayburn W.F.
      • Sokkary N.
      • Clokey D.E.
      Consequences of routine delivery at 38 weeks for A-2 gestational diabetes.
      Three recent retrospective analyses found no increase in operative delivery with induction of labor
      • Stock S.J.
      • Ferguson E.
      • Duffy A.
      • Ford I.
      • Chalmers J.
      • Norman J.E.
      Outcomes of elective induction of labor compared with expectant management: population based study.
      and a decrease in the cesarean delivery rate among nulliparous women delivering at 39-42 weeks' gestational age
      • Cheng Y.W.
      • Kaimal A.J.
      • Snowden J.M.
      • Nicholson J.M.
      • Caughey A.B.
      Induction of labor compared to expectant management in low-risk women and associated perinatal outcomes.
      and all women delivering in the term period (37-40 weeks).
      • Darney B.G.
      • Snowden J.M.
      • Cheng Y.W.
      • et al.
      Elective induction of labor at term compared with expectant management: maternal and neonatal outcomes.
      Cheng et al
      • Cheng Y.W.
      • Kaimal A.J.
      • Snowden J.M.
      • Nicholson J.M.
      • Caughey A.B.
      Induction of labor compared to expectant management in low-risk women and associated perinatal outcomes.
      also reported improvement in other associated neonatal morbidities including meconium aspiration, 5-minute Apgar <7, infection, ventilator use, composite morbidity, and neonatal intensive care unit (ICU) admission with induction at 39 weeks' gestation. Using discharge and birth certificate data, Darney et al
      • Darney B.G.
      • Snowden J.M.
      • Cheng Y.W.
      • et al.
      Elective induction of labor at term compared with expectant management: maternal and neonatal outcomes.
      also recently found a reduction in cesarean deliveries with induction of labor compared to expectant management at 37, 38, 39, and 40 weeks of gestation. Importantly, Darney et al
      • Darney B.G.
      • Snowden J.M.
      • Cheng Y.W.
      • et al.
      Elective induction of labor at term compared with expectant management: maternal and neonatal outcomes.
      also reported no increase in neonatal ICU admission or respiratory distress with elective induction of labor, including those performed at 37 and 38 weeks of pregnancy.
      To date, few studies have evaluated maternal and neonatal outcomes with elective induction of labor encompassing all of the term period in a low-risk obstetric population.
      • Darney B.G.
      • Snowden J.M.
      • Cheng Y.W.
      • et al.
      Elective induction of labor at term compared with expectant management: maternal and neonatal outcomes.
      • Osmundson S.
      • Ou-Yang R.J.
      • Grobman W.A.
      Elective induction compared with expectant management in nulliparous women with an unfavorable cervix.
      Only 2 small, single-site studies included data on cervical status,
      • Osmundson S.
      • Ou-Yang R.J.
      • Grobman W.A.
      Elective induction compared with expectant management in nulliparous women with an unfavorable cervix.
      • Osmundson S.
      • Ou-Yang R.J.
      • Grobman W.A.
      Elective induction compared with expectant management in nulliparous women with a favorable cervix.
      while the majority of the available literature did not have this important obstetric variable available for their analyses. As national attention has identified >39 weeks as the optimal time for delivery for low-risk women due to a reported decrease in neonatal risks, specifically respiratory morbidity,
      • Consortium on Safe Labor
      • Hibbard J.U.
      • Wilkins I.
      • Sun L.
      • et al.
      Respiratory morbidity in late preterm births.
      • Tita A.T.
      • Landon M.B.
      • Spong C.Y.
      • et al.
      Timing of elective repeat cesarean delivery at term and neonatal outcomes; Eunice Kennedy Shriver NICHD Maternal-Fetal Medicine Units Network.
      • Reddy U.M.
      • Ko C.W.
      • Raju T.N.
      • Willinger M.
      Delivery indications at late-preterm gestations and infant mortality rates in the United States.
      a comprehensive evaluation of the risks and benefits of elective delivery by week are crucial. As previous investigations have noted a consistent pattern of a reduction in cesarean delivery with induction of labor as early as 37 weeks of gestation without a reciprocal increase in neonatal morbidity, it is imperative for additional investigations to either confirm or refute this observation. Therefore, we sought to evaluate the mode of delivery and maternal and neonatal morbidities in low-risk patients whose labor was electively induced or expectantly managed at term using a national obstetric records database that contained detailed information regarding maternal medical history, indications for induction, and cervical examinations.

      Materials and Methods

      Study population

      We selected our study cohort from the database of the Consortium on Safe Labor, a study conducted by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institutes of Health.
      • Zhang J.
      • Troendle J.
      • Reddy U.M.
      • et al.
      Contemporary cesarean delivery practice in the United States.
      In brief, this was a retrospective cross-sectional study involving deliveries from 2002 through 2008 from 12 clinical centers and 19 hospitals representing 9 American Congress of Obstetricians and Gynecologists (ACOG) districts. The population was then standardized by assigning a weight to each subject using ACOG district, maternal race/ethnicity, parity, and plurality based on 2004 national data.
      • Zhang J.
      • Troendle J.
      • Reddy U.M.
      • et al.
      Contemporary cesarean delivery practice in the United States.
      • Martin J.A.
      • Hamilton B.E.
      • Sutton P.D.
      • Ventura S.J.
      • Menacker F.
      • Kirmeyer S.
      Births: final data for 2004.
      Institutional review board approval was obtained for this analysis.
      The Figure presents the flow diagram for our cohort selection. From the initial data set of all nulliparous and multiparous women presenting for delivery, we started with the first singleton pregnancy for each woman (233,736). We then limited the group to term gestations of 37-42 weeks' gestational age (178,575) and in vertex presentation (155,848). To limit confounding, we excluded all those with a prior uterine scar or planned (elective) cesarean delivery (136,014). Finally, we excluded those with chronic maternal conditions that may lead to indicated delivery, including diabetes mellitus, chronic hypertension, cardiovascular disease, placental previa, or human immunodeficiency virus–positive status. Women who developed a pregnancy-related complication such as preeclampsia, gestational hypertension, abruption, or fetal compromise were included in the final cohort of 131,243 low-risk women. If these complications developed antepartum, the patients were no longer a candidate for an elective induction of labor, and they were included only in the expectant management arm of the study. We then identified women with an elective induction of labor.
      • Laughon S.K.
      • Zhang J.
      • Grewal J.
      • et al.
      Induction of labor in a contemporary obstetric cohort.
      A predefined variable for induction of labor was coded when either the patient's electronic medical record indicated that there was an induction and/or a method or start time for induction. This variable did not include women receiving only labor augmentation or those without at least 2 vaginal examinations in the labor progression database. Inductions were categorized as “indicated,” “elective,” and “no recorded indication.” Indications for induction included all potential maternal, fetal, or obstetric complications of pregnancy. If a site indicated that the induction was elective, no other indications for induction were provided, and there were no other obstetric, fetal, or maternal conditions complicating the pregnancy, then the induction was designated “elective.” All other deliveries, including the “no recorded indication” category were included in the expectant management group. Method of labor induction included all methods for cervical ripening and induction with multiple methods was allowed.
      Figure thumbnail gr1
      FigureFlow diagram of cohort selection and distribution of subjects by week of pregnancy
      The selection of our low-risk term cohort and the distribution of our final cohort into those electively induced or expectantly managed by week of pregnancy.
      HIV, human immunodeficiency virus.
      Gibson. Outcomes in electively induced low-risk term pregnancies. Am J Obstet Gynecol 2014.

      Study outcomes

      Subjects were divided by week of gestational age at delivery (Figure). Those with an induction of labor coded as “elective” were the cases at each week of gestation (elective induction of labor). Those not electively induced and who delivered after that week of gestation were considered to be expectantly managed in that week of gestation. For example, the women who delivered in their 37th week of gestation after an elective induction were compared to those who delivered in their ≥38th week as they had been expectantly managed in their 37th week. Mode of delivery was categorized as a nonoperative vaginal delivery, an operative vaginal delivery (requiring vacuum or forceps assistance), or cesarean section.
      Given the limitations of pregnancy dating and the size of our data set, we chose to evaluate gestational age by week rather than day. We acknowledge that many women who are expectantly managed may have either a spontaneous labor or indicated induction in the same week. Therefore, we did a secondary analysis comparing those with elective induction of labor to those expectantly managed, but ultimately delivering within the same week.
      The primary outcome of interest was mode of delivery. Secondary outcomes included composites for maternal and neonatal comorbidities. Maternal outcomes included bleeding (blood products, abruption, postpartum hemorrhage, uterine rupture, hysterectomy), maternal ICU admission or death, infections (intrapartum fevers, chorioamnionitis, endomyometritis, wound separation), lacerations (third- or fourth-degree perineal, sulcal, or cervical), and shoulder dystocia. Neonatal outcomes included a composite of major comorbidities (birth injuries, sepsis, pneumonia, intraventricular hemorrhage, aspiration, hypoxic ischemic encephalopathy, respiratory distress syndrome, seizures, oliguria, myocardial injury, ventilator use, continuous positive airway pressure use, transient tachypnea of the newborn, transfusions, or surfactant use), a composite of respiratory morbidities (oxygen use, continuous positive airway pressure use, transient tachypnea of the newborn, or surfactant administration), or perinatal death (intrauterine fetal demise or neonatal demise).
      To adjust for possible confounding factors on successful induction of labor and maternal and neonatal outcomes, logistic regression was performed. We controlled for maternal age, race/ethnicity, parity, body mass index at delivery, insurance status, type of hospital, and modified Bishop score at delivery admission. As only 51% (67,257) of patients had all 5 components of the Bishop score reported, while 84% (110,432) had information on cervical dilation, effacement, and station available, we used a modified Bishop score to determine cervical ripeness. We defined an unripe cervix as a modified Bishop score ≤4.
      • Laughon S.K.
      • Zhang J.
      • Grewal J.
      • et al.
      Induction of labor in a contemporary obstetric cohort.

      Statistical analysis

      Given that this is a descriptive analysis with very large sample size, power calculations were not performed. The χ2 and t tests were used where appropriate. Demographic factors were controlled for with logistic regression. Centers with >5% missing data for an outcome were removed from the analysis on that specific outcome. We performed all analyses using statistical software (SAS, version 9.3; SAS Institute Inc, Cary, NC).

      Results

      Patients

      Our low-risk patient population included 131,243 women. Table 1 presents the maternal demographic characteristics for the entire cohort and by maternal parity. Our patients were nearly half nulliparous with 88% being younger than 35 years at delivery. The majority were Caucasian (51.7%) and overweight or obese (mean body mass index: 30.3 ± 5.8 kg/m2). Only 1.2% of patients were self-paying with >90% delivering at a teaching hospital (40.2% university and 50.8% community teaching hospitals). In all, 57% had a favorable cervix on admission. On average, subjects delivered at 39.3 ± 1.1 weeks' gestational age.
      Table 1Demographic characteristics
      VariableTotal (131,243)Nulliparous (64,376)Parous (66,867)
      No.%No.%No.%
      Maternal age, y
       ≤1914,01210.712,27019.117422.6
       20-34100,87576.947,12273.253,75380.4
       ≥3516,19312.349177.611,27616.9
       Missing1630.1670.1960.1
      Race/ethnicity
       African American26,26320.013,05020.313,21319.8
       Caucasian67,88551.732,61250.735,27352.8
       Hispanic22,08016.810,32516.011,75517.6
       Asian57184.434065.323123.5
       Other92977.149837.743146.5
      BMI at delivery, kg/m2
       Normal/underweight (<25.0)16,33012.4854313.3778711.6
       Overweight (25.0-29.9)43,73533.321,97234.121,76332.5
       Obese (30.0-34.9)28,59021.813,50021.015,09022.6
       Morbid obesity (>35.0)18,97214.5881513.710,15715.2
       Missing23,61618.011,54617.912,07018.0
      Insurance
       Private75,20057.336,49156.738,70957.9
       Public38,73229.519,05629.619,67629.4
       Self-pay15171.27501.27671.1
       Other/missing15,79412.0807912.6771511.5
      Hospital type
       University teaching52,76940.227,76343.125,00637.4
       Community teaching66,60550.831,94349.634,66251.8
       Community nonteaching11,8699.046707.3719910.8
      Modified Bishop score
       ≤455,31142.127,93043.427,38141.0
       >475,93257.936,44656.639,48659.0
      Gestational age at delivery, wk
       3712,4709.555938.7687710.3
       3827,44920.912,21319.015,23622.8
       3944,97034.319,96531.025,00537.4
       4034,26226.119,15829.815,10422.6
       4112,0929.2744711.646456.9
      Elective induction, wk
       372240.2720.11520.2
       3813441.04040.69401.4
       3975635.815762.559879.0
       4041113.121243.319873.0
      BMI, body mass index.
      Gibson. Outcomes in electively induced low-risk term pregnancies. Am J Obstet Gynecol 2014.
      The distribution of elective deliveries by week of gestation and parity is also presented in Table 1. Ten percent of the total cohort (n = 13,242) had an elective induction of labor with 57% of all elective inductions performed in the 39th week of gestation. The majority of elective inductions were parous (68%), particularly at 37, 38, and 39 weeks of gestation. The Figure shows the number of electively induced deliveries, nonelectively induced deliveries and expectantly managed subjects for each week of gestation.

      Study outcomes

      Table 2 presents the findings of the primary outcome, mode of delivery. Nonoperative vaginal delivery occurred more often in the electively induced group when compared to the expectantly managed group at each week of gestation. Additionally, the frequency of both operative vaginal delivery and cesarean delivery was significantly lower for the electively induced group at each gestational age in both nulliparous and multiparous patients with either a favorable or unfavorable cervical status on admission. The odds of a cesarean delivery after an elective induction of labor vs expectant management were lower at each week of gestation after controlling for possible confounding factors in a logistic regression. (Adjusted odds ratio for births at 37 weeks in nulliparous patients with an unfavorable cervix = 0.40 [95% CI, 0.18–0.88]; 38 weeks = 0.65 [95% CI, 0.49–0.85]; 39 weeks = 0.47 [95% CI, 0.38–0.57]; 40 weeks = 0.69 [95% CI, 0.59–0.81]; in multiparous patients with a favorable cervix at: 38 weeks = 0.42 [95% CI, 0.16–1.14]; 39 weeks = 0.35 [95% CI, 0.23–0.53]; 40 weeks = 0.54 [95% CI, 0.30–0.97].) The comparison of the primary outcome for those electively induced compared to those who delivered within the same week (without elective induction) demonstrated similar findings (Supplemental Table 1).
      Table 2Mode of delivery by week of elective induction of labor compared to those expectantly managed by parity and modified Bishop score
      Nulliparous
      Nonoperative vaginal delivery
      WkNulliparous and unfavorableWkNulliparous and favorable
      eIOLExpaOR95% CIeIOLExpaOR95% CI
      No.%No.%No.%No.%
      3733/4376.712,381/21,52057.53724/2885.724,503/33,48673.2
      38190/28566.79597/17,09956.13889/11080.918,986/26,35271.7
      39420/60269.85524/10,40453.139720/95575.49830/14,20169.2
      40629/109457.51759/350950.140634/91769.12205/329267.0
      Operative vaginal delivery
      WkNulliparous and unfavorableWkNulliparous and favorable
      eIOLExpaOR95% CIeIOLExpaOR95% CI
      No.%No.%No.%No.%
      372/434.71786/21,5208.30.4440.106–1.861373/2810.74040/33,48612.10.8090.242–2.707
      3814/2854.91449/17,0998.50.4930.285–0.8543812/11010.93224/26,35212.20.7690.418–1.412
      3940/6026.6876/10,4048.40.5220.373–0.73239157/95516.41756/14,20112.41.0110.841–1.215
      40112/109410.2268/35097.60.8650.669–1.12040167/91718.2392/329211.91.1440.919–1.424
      Cesarean delivery
      WkNulliparous and unfavorableWkNulliparous and favorable
      eIOLExpaOR95% CIeIOLExpaOR95% CI
      No.%No.%No.%No.%
      378/4318.67353/21,52034.20.4020.183–0.884371/283.64943/33,48614.80.1640.022–1.228
      3881/28528.46053/17,09935.40.6470.494–0.847389/1108.24142/26,35215.70.4300.213–0.864
      39142/60223.64004/10,40438.50.4660.381–0.5693978/9558.22615/14,20118.40.4970.389–0.633
      40353/109432.31482/350942.30.6890.588–0.80740116/91712.7695/329221.10.6940.551–0.874
      Multiparous
      Nonoperative vaginal delivery
      WkMultiparous and unfavorableWkMultiparous and favorable
      eIOLExpaOR95% CIeIOLExpaOR95% CI
      No.%No.%No.%No.%
      3783/8597.717,334/19,78287.63762/6496.933,345/35,57293.7
      38439/47492.612,961/14,81587.538413/42996.324,638/26,40093.3
      392006/219761.36036/703385.8393446/367793.710,042/10,83092.7
      40820/91289.91716/203384.440885/95992.31963/212192.6
      Operative vaginal delivery
      WkMultiparous and unfavorableWkMultiparous and favorable
      eIOLExpaOR95% CIeIOLExpaOR95% CI
      No.%No.%No.%No.%
      370/850.0733/19,7823.7372/643.11286/35,5723.60.7880.192–3.238
      3812/4742.5561/14,8153.80.5500.307–0.9853812/4292.81010/26,4003.80.6100.342–1.089
      39125/21975.7246/70333.51.1390.879–1.47739204/36775.6402/10,8303.71.2421.017–1.516
      4046/9125.067/20333.31.0910.701–1.6984058/9596.167/21213.21.6941.123–2.555
      Cesarean delivery
      WkMultiparous and unfavorableWkMultiparous and favorable
      eIOLExpaOR95% CIeIOLExpaOR95% CI
      No.%No.%No.%No.%
      372/852.41715/19,7828.70.2650.064–1.088370/640.0941/35,5722.7
      3823/4744.91293/14,8158.70.5530.360–0.850384/4290.9752/26,4002.90.4210.156–1.137
      3966/21973.0751/703310.70.3460.262–0.4563927/36770.7386/10,8303.60.3520.231–0.534
      4046/9125.0250/203312.30.4370.307–0.6224016/9591.791/2121+A484.30.5360.297–0.968
      aOR is of the outcome compared to vaginal delivery for eIOL with expectant as the referent controlling for maternal age, race/ethnicity, body mass index at delivery, insurance, and type of hospital.
      aOR, adjusted odds ratio; CI, confidence interval; eIOL, elective induction of labor; exp, expectant management.
      Gibson. Outcomes in electively induced low-risk term pregnancies. Am J Obstet Gynecol 2014.
      As the decision to deliver a patient, or allow a pregnancy to continue until indicated delivery or spontaneous labor occurs, encompasses many potential outcomes for the mother and neonate, we next evaluated several secondary maternal and neonatal outcomes (Tables 3 and 4). The risk of maternal bleeding complications, ICU admissions, or death was overall similar between the 2 groups after adjustment for confounding factors. Elective induction of labor appeared to be protective against maternal infection at each week of gestation for both nulliparous and multiparous patients (nulliparous patients at: 37 weeks = adjusted odds ratio, 0.35 [95% CI, 0.13–0.95]; 38 weeks = 0.35 [95% CI, 0.23–0.53]; 39 weeks = 0.41 [95% CI, 0.33–0.50]; 40 weeks = 0.45 [95% CI, 0.38–0.55]; in multiparous patients at: 37 weeks = 0.21 [95% CI, 0.03–1.54]; 38 weeks = 0.20 [95% CI, 0.08–0.48]; 39 weeks = 0.34 [95% CI, 0.25–0.47]; 40 weeks = 0.72 [95% CI, 0.47–1.08]). The frequency of a significant obstetrical laceration was lower with elective induction in nulliparous patients at 37 and 38 weeks and in multiparous patients at 39 and 40 weeks, but only significant for the multiparous patients after adjustment. Elective induction was protective against shoulder dystocia at 38 weeks of gestation for multiparous patients. These results are similar to the findings for women electively induced compared to those delivering in the same week (Supplemental Table 2).
      Table 3Secondary outcomes of maternal morbidity by week of elective induction of labor compared to those expectantly managed divided by parity
      NulliparousMaternal bleeding complications
      WkeIOLExpaOR95% CI
      No.%No.%
      371/651.52990/42,2307.10.2110.029–1.521
      3812/3683.32357/33,2157.10.4140.232–0.740
      39119/14018.51300/18,5357.01.0100.827–1.233
      40127/15698.1317/50956.20.9870.784–1.243
      WkMaternal intensive care admission or death
      eIOLExpaOR95% CI
      No.%No.%
      370/720.097/44,7280.2
      380/3990.069/35,1170.2
      390/1.5660.045/19,6000.2
      404/20600.211/51240.20.9840.273–3.552
      WkMaternal infections
      eIOLExpaOR95% CI
      No.%No.%
      374/685.97155/46,97815.20.3450.125–0.952
      3823/3826.05886/37,10915.90.3470.227–0.530
      3997/15406.33591/20,84417.20.4050.328–0.500
      40152/18818.11092/560019.50.4540.377–0.546
      WkThird- or fourth-degree perineal or sulcal lacerations
      eIOLExpaOR95% CI
      No.%No.%
      375/726.96206/58,78310.60.7670.308–1.910
      3835/4048.74997/46,57010.70.9690.683–1.377
      39173/157611.02902/26,60510.90.8960.759–1.057
      40235/212411.1790/744710.60.9780.829–1.153
      WkShoulder dystocia
      eIOLExpaOR95% CI
      No.%No.%
      370/720.0697/56,4791.2
      382/4040.5580/44,6711.30.3570.088–1.439
      3927/15761.7341/25,4021.31.2920.865–1.929
      4029/21241.495/69971.41.1340.732–1.757
      MultiparousMaternal bleeding complications
      WkeIOLExpaOR95% CI
      No.%No.%
      379/1326.83269/44,6617.30.8960.453–1.772
      3851/8226.22382/33,1847.20.7030.526–0.939
      39597/556810.7802/13,8395.81.3601.199–1.542
      40121/15717.7165/31525.21.0690.810–1.412
      WkMaternal intensive care admission or death
      eIOLExpaOR95% CI
      No.%No.%
      371/1490.4140/46,3450.33.5960.482–26.832
      381/9320.1107/34,1190.30.7550.104–5.498
      399/59710.249/13,7970.41.6020.679–3.779
      401/19350.115/29480.50.4020.050–3.206
      WkMaternal infections
      eIOLExpaOR95% CI
      No.%No.%
      371/1410.71561/49,0793.20.2140.030–1.536
      385/8830.61211/36,6373.30.1960.081–0.475
      3947/58640.8632/15,5204.10.3400.248–0.466
      4032/17981.8151/35164.30.7170.474–1.083
      WkThird- or fourth-degree perineal or sulcal lacerations
      eIOLExpaOR95% CI
      No.%No.%
      375/1523.31687/59,9902.81.2790.523–3.129
      3821/9402.21286/44,7542.90.8460.546–1.312
      39116/59871.9601/19,7493.00.6120.491–0.764
      4043/19872.2136/46452.90.6690.457–0.977
      WkShoulder dystocia
      eIOLExpaOR95% CI
      No.%No.%
      370/1520.01084/57,3061.9
      388/9400.9878/42,7102.10.4240.2110.856
      39114/59871.9419/18,6352.30.9810.7761.240
      4048/19872.493/42862.21.1940.8091.761
      aOR is of the outcome compared to vaginal delivery for eIOL with expectant as the referent controlling for maternal age, race/ethnicity, body mass index at delivery, insurance, type of hospital, and modified Bishop score.
      aOR, adjusted odds ratio; CI, confidence interval; eIOL, elective induction of labor; exp, expectant management.
      Gibson. Outcomes in electively induced low-risk term pregnancies. Am J Obstet Gynecol 2014.
      Table 4Secondary outcomes of neonatal morbidity by week of elective induction of labor compared to those expectantly managed divided by parity
      NulliparousNeonatal complication composite
      WkeIOLExpaOR95% CI
      No.%No.%
      375/726.95033/58,7838.60.7820.314–1.947
      3816/4044.04049/46,5708.70.4330.262–0.716
      39109/15766.92451/26,6059.20.7500.613–0.917
      40137/21246.5743/744710.00.6520.535–0.795
      WkNeonatal respiratory complications
      eIOLExpaOR95% CI
      No.%No.%
      371/721.41799/54,4553.30.3710.051–2.674
      387/3981.81467/43,1103.40.4650.219–0.986
      3930/15531.9863/24,5083.50.5400.373–0.783
      4046/19632.3265/68330.90.5890.423–0.821
      WkPerinatal death
      eIOLExpaOR95% CI
      No.%No.%
      370/720.0202/56,4790.4
      380/4040.0158/44,6710.4
      392/15760.188/25,4020.40.3480.085–1.424
      406/21240.317/69970.21.0910.398–2.992
      MultiparousNeonatal complication composite
      WkeIOLExpaOR95% CI
      No.%No.%
      379/1525.93120/59,9905.21.1970.608–2.354
      3844/9404.72213/44,7544.90.9810.721–1.334
      39179/59873.0988/19,7495.00.5900.494–0.705
      4075/19873.8232/46455.00.7560.564–1.012
      WkNeonatal respiratory complications
      eIOLExpaOR95% CI
      No.%No.%
      378/1455.51107/55,2842.02.8971.412–5.945
      3814/8981.6797/41,3061.90.8270.484–1.413
      3960/58841.0365/18,0372.00.5740.424–0.778
      4027/18691.593/41982.20.6850.424–1.109
      WkPerinatal death
      eIOLExpaOR95% CI
      No.%No.%
      370/1520.0195/57,3060.3
      380/9400.0122/42,7100.3
      3911/59870.257/18,6350.30.7810.376–1.625
      403/19870.214/42860.30.6300.163–2.429
      aOR is of the outcome compared to vaginal delivery for eIOL with expectant as the referent controlling for maternal age, race/ethnicity, body mass index at delivery, insurance, type of hospital, and modified Bishop score.
      aOR, adjusted odds ratio; CI, confidence interval; eIOL, elective induction of labor; exp, expectant management.
      Gibson. Outcomes in electively induced low-risk term pregnancies. Am J Obstet Gynecol 2014.
      The risk of adverse outcomes for the neonate is presented in Table 4. There were no significant differences in the frequency of composite neonatal morbidity for electively induced women at 37 weeks compared to the expectantly managed group. By 38 weeks, elective induction was associated with a reduction in composite neonatal morbidity in nulliparous patients and a trend toward reduction in multiparous patients. Similar results were observed for only respiratory morbidities. The comparison of neonatal morbidities for those who delivered within the same week as those who were electively induced is presented in Supplemental Table 3. There was a higher composite neonatal morbidity for subjects who delivered without elective induction, but still within the same week compared to those electively induced. Similar results were observed for respiratory morbidities.

      Comment

      Using a cohort of low-risk pregnancies within the Consortium on Safe Labor database, we examined maternal and neonatal outcomes for women who were electively induced compared to those expectantly managed at each week of term gestation. For our primary outcome of mode of delivery, we observed a reduction in cesarean section with elective induction, regardless of week of gestation, parity, or cervical examination. For secondary outcomes including maternal and neonatal morbidity, no outcome was shown to be worse with elective induction. Conversely, several maternal outcomes including infectious morbidity, obstetrical lacerations, and shoulder dystocia were reduced with induction of labor. For those electively induced, we observed a reduction in composite neonatal morbidities with induction of labor at 38, 39, and 40 weeks' gestation.
      For decades, induction of labor was reported to be associated with adverse maternal and fetal outcomes, particularly for nulliparous women with an unfavorable cervical examination <39 weeks' gestation.
      • Glantz J.C.
      Elective induction vs spontaneous labor: associations and outcomes.
      However, many of these investigations did not compare induction to the only other clinical option: expectant management. In this analysis, we chose to compare women electively induced at a given week of gestation to those managed until the next week of pregnancy or later as this attempts to capture both the risks and benefits of either choice. Our primary finding of a decreased odds of cesarean delivery with elective induction corroborate the findings of more recent investigations
      • Caughey A.B.
      • Nicholson J.M.
      • Cheng Y.W.
      • Lyell D.J.
      • Washington A.E.
      Induction of labor and cesarean delivery by gestational age.

      The National Institute of Child Health and Human Development Network of Maternal-Fetal Medicine Units. A clinical trial of induction of labor versus expectant management in postterm pregnancy. Am J Obstet Gynecol 1994;170:716-23.

      • Cole R.A.
      • Howie P.W.
      • Macnaughton M.C.
      Elective induction of labor: randomized prospective trial.
      • Hannah M.E.
      • Hannah W.J.
      • Hellmann J.
      • Hewson S.
      • Milner R.
      • Willan A.
      Induction of labor as compared with serial antenatal monitoring in post-term pregnancy: a randomized controlled trial; the Canadian Multicenter Post-term Pregnancy Trial Group.
      • Caughey A.B.
      • Sundaram V.
      • Kaimal A.J.
      • et al.
      Systematic review: elective induction of labor versus expectant management of pregnancy.
      • Koopmans C.M.
      • Bijlenga D.
      • Groen H.
      • et al.
      HYPITAT Study Group
      Induction of labor versus expectant monitoring for gestational hypertension or mild pre-eclampsia after 36 weeks' gestation (HYPITAT): a multicenter, open-label randomized controlled trial.
      • Boers K.E.
      • Vijgen S.M.
      • Bijlenga D.
      • et al.
      DIGITAT Study Group
      Induction versus expectant monitoring for intrauterine growth restriction at term: randomized equivalence trial (DIGITAT).
      • Kjos S.L.
      • Henry O.A.
      • Montoro M.
      Insulin-requiring diabetes in pregnancy: a randomized trial of active induction of labor and expectant management.
      • Rayburn W.F.
      • Sokkary N.
      • Clokey D.E.
      Consequences of routine delivery at 38 weeks for A-2 gestational diabetes.
      • Stock S.J.
      • Ferguson E.
      • Duffy A.
      • Ford I.
      • Chalmers J.
      • Norman J.E.
      Outcomes of elective induction of labor compared with expectant management: population based study.
      • Cheng Y.W.
      • Kaimal A.J.
      • Snowden J.M.
      • Nicholson J.M.
      • Caughey A.B.
      Induction of labor compared to expectant management in low-risk women and associated perinatal outcomes.
      • Darney B.G.
      • Snowden J.M.
      • Cheng Y.W.
      • et al.
      Elective induction of labor at term compared with expectant management: maternal and neonatal outcomes.
      • Osmundson S.
      • Ou-Yang R.J.
      • Grobman W.A.
      Elective induction compared with expectant management in nulliparous women with an unfavorable cervix.
      • Osmundson S.
      • Ou-Yang R.J.
      • Grobman W.A.
      Elective induction compared with expectant management in nulliparous women with a favorable cervix.
      that were based on administrative data and birth certificate registries. The data reported herein move this area of study forward as the Consortium on Safe Labor data set is large with detailed medical record data, including cervical examinations, allowing for analysis of morbidity by week of gestation and by cervical ripeness at delivery admission. Additionally, we observed that induction of labor was associated with a lower risk of maternal infectious complications, shoulder dystocia, and neonatal composite morbidities. These data paint a consistent picture that induction is potentially associated with several other improvements in outcomes for mom and baby, throughout the term period.
      Prior publications have reported on newborn morbidities by week of delivery
      • Consortium on Safe Labor
      • Hibbard J.U.
      • Wilkins I.
      • Sun L.
      • et al.
      Respiratory morbidity in late preterm births.
      • Tita A.T.
      • Landon M.B.
      • Spong C.Y.
      • et al.
      Timing of elective repeat cesarean delivery at term and neonatal outcomes; Eunice Kennedy Shriver NICHD Maternal-Fetal Medicine Units Network.
      • Reddy U.M.
      • Ko C.W.
      • Raju T.N.
      • Willinger M.
      Delivery indications at late-preterm gestations and infant mortality rates in the United States.
      and have consistently found lower neonatal morbidities with increasing week of gestation at term. However in these analyses morbidities are only attributed to the week of birth without consideration of other potential causes, including the risks of waiting for a later gestational age. Obstetric complications can occur while a patient is attempting to obtain a later gestational age including: abruption, cord prolapse, infection, prolonged rupture of the membranes, and maternal hypertensive disease. These and other conditions have their own associated maternal and neonatal morbidities as well as the burden of time on labor and delivery units and the costs of associated interventions. Our finding of a reduction in maternal and neonatal morbidities with elective induction suggests that expectant management of a term pregnancy is not a risk-free proposition. We hypothesize this observation may be related to the potential complications that can occur for any gravid while waiting for labor or a later gestational age.
      Our data have several limitations. First, while we attempted to compare elective induction vs expectantly managed women, this was not a randomized trial. This study uses a cross-sectional data set to address a longitudinal question. We attempted to control for known confounding variables in our multivariate analysis, yet unmeasured factors or potential selection bias such as the asynchronous timing of the cervical examinations on delivery admission may be possible. It may be that only women who were considered more likely to be successfully induced were electively induced, and women who were considered unlikely to be successful were not (healthy user bias). Therefore, we may only be observing that clinicians are astute at determining which women are low risk and will be successfully induced. However, as this analysis is based on medical records data (and not administrative data), we use the best data possible short of having an observer at each delivery. Additionally, our elective induction cohort at 37 weeks may be too small to draw firm conclusions about risks or benefits, but the findings are consistent with the rest of the data at later weeks.
      We observed a lower neonatal morbidity in those electively induced with increasing week of gestation, consistent with papers that have evaluated neonatal morbidity by delivery age alone.
      • Consortium on Safe Labor
      • Hibbard J.U.
      • Wilkins I.
      • Sun L.
      • et al.
      Respiratory morbidity in late preterm births.
      • Tita A.T.
      • Landon M.B.
      • Spong C.Y.
      • et al.
      Timing of elective repeat cesarean delivery at term and neonatal outcomes; Eunice Kennedy Shriver NICHD Maternal-Fetal Medicine Units Network.
      • Reddy U.M.
      • Ko C.W.
      • Raju T.N.
      • Willinger M.
      Delivery indications at late-preterm gestations and infant mortality rates in the United States.
      Yet, our data highlight that this observation can lead to misleading conclusions about the best gestational age for delivery when the risks of expectant management are excluded from the analysis. In light of the findings from retrospective studies such as this paper, the NICHD and the Maternal-Fetal Medicine Units Network is beginning a randomized trial of induction versus expectant management (ARRIVE) at 39 weeks' gestation. We hope this prospective trial will add clarity to the issue of mode of delivery in the full term period, though we believe this paper and the paper by Darney et al
      • Darney B.G.
      • Snowden J.M.
      • Cheng Y.W.
      • et al.
      Elective induction of labor at term compared with expectant management: maternal and neonatal outcomes.
      demonstrate the need to consider lowering gestational age at study entry to earlier in the term period.
      Finally, the interpretation of our findings warrants caution. These data do not attempt to define what the best gestational age is for delivery at term. Rather, we submit that our results demonstrate that when maternal and newborn outcomes are analyzed through the prism of the true clinical alternatives of induction or waiting, the findings may be drastically different than what has been reported previously. Clearly, these data suggest that outcomes for mom and baby are complex with competing interests. Evaluations that only consider differences in observed neonatal morbidities by week of delivery paint an incomplete picture as they do not account for the risks of waiting. As such, we propose that the decision of timing of delivery or best gestational age for delivery has not been fully answered by current data or analyses. As the majority of women in the United States deliver at term, they deserve better data and analysis including large randomized trials, which are powered to accurately account for the potential risks and benefits of delivery vs non delivery for both patients.

      Acknowledgments

      The authors would like to thank S. Katherine Laughon, MD, MS (Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD) and Jun Zhang, PhD (Ministry of Education and Shanghai Key Laboratory of Children's Environmental Health, Xinhua Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China) for their assistance in study design, data analysis, and manuscript editing. Additionally, we would like to thank Stephen Myers, DO (Division of Maternal Fetal Medicine, Department of Obstetrics and Gynecology, MetroHealth Medical Center–Case Western Reserve University, Cleveland, OH), for his intellectual contribution to this topic.
      The Consortium on Safe Labor was funded by the Intramural Research Program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institutes of Health, through Contract No. HHSN267200603425C. Institutions involved in the Consortium include, in alphabetical order: Baystate Medical Center, Springfield, MA; Cedars-Sinai Medical Center Burnes Allen Research Center, Los Angeles, CA; Christiana Care Health System, Newark, DE; EMMES Corporation, Rockville, MD (Data Coordinating Center); Georgetown University Hospital, MedStar Health, Washington, DC; Indiana University Clarian Health, Indianapolis, IN; Intermountain Healthcare and the University of Utah, Salt Lake City, UT; Maimonides Medical Center, Brooklyn, NY; MetroHealth Medical Center, Cleveland, OH; Summa Health System, Akron City Hospital, Akron, OH; University of Illinois at Chicago, Chicago, IL; University of Miami, Miami, FL; and University of Texas Health Science Center at Houston, Houston, TX. The named authors alone are responsible for the views expressed in this manuscript, which does not necessarily represent the decisions or the stated policy of the NICHD.

      Appendix

      Supplemental Table 1Mode of delivery by week of elective induction of labor compared to those expectantly managed within the same week of delivery by parity and modified Bishop score
      Nulliparous
      Nonoperative vaginal delivery
      WkNulliparous and unfavorableWkNulliparous and favorable
      eIOLExpaOR95% CIeIOLExpaOR95% CI
      No.%No.%No.%No.%
      3733/4376.71502/328865.73724/2885.72366/293280.7
      38190/28566.72594/413662.73889/11080.95428/702477.3
      39420/60269.83653/609360.039720/95575.48436/11,19675.4
      40629/109457.53136/580154.140634/91769.16991/999270.0
      Operative vaginal delivery
      WkNulliparous and unfavorableWkNulliparous and favorable
      eIOLExpaOR95% CIeIOLExpaOR95% CI
      No.%No.%No.%No.%
      372/434.7161/22887.00.5620.132–2.402373/2810.7324/293211.10.9780.290–3.301
      3814/2854.9323/41367.80.5310.302–0.9313812/11010.9804/702411.50.8630.468–1.594
      3940/6026.6533/60938.80.5830.414–0.82139157/95516.41311/11,19611.71.2091.002–1.458
      40112/109410.2496/58018.60.8300.655–1.05040167/91718.21197/999212.01.2151.006–1.467
      Cesarean delivery
      WkNulliparous and unfavorableWkNulliparous and favorable
      eIOLExpaOR95% CIeIOLExpaOR95% CI
      No.%No.%No.%No.%
      378/4318.6625/228827.30.5580.250–1.241371/283.6242/29328.30.3270.043–2.459
      3881/28528.41219/413629.50.8480.641–1.122389/1108.2792/702411.30.5930.293–1.200
      39142/60223.61907/609331.30.6320.514–0.7763978/9558.21449/11,19612.90.7350.574–0.942
      40353/109432.32169/580137.40.8440.727–0.98140116/91712.71804/999218.00.8580.694–1.062
      Multiparous
      Nonoperative vaginal delivery
      WkMultiparous and unfavorableWkMultiparous and favorable
      eIOLExpaOR95% CIeIOLExpaOR95% CI
      No.%No.%No.%No.%
      3783/8597.72142/243787.93762/6496.93660/385095.1
      38439/47492.63934/449387.638413/42996.38294/874394.9
      392006/219761.34919/558588.1393446/367793.711,150/11,89393.8
      40820/91289.93500/408885.640885/95992.37194/775092.8
      Operative vaginal delivery
      WkMultiparous and unfavorableWkMultiparous and favorable
      eIOLExpaOR95% CIeIOLExpaOR95% CI
      No.%No.%No.%No.%
      370/850.079/24373.2372/643.1104/38502.71.0120.243–4.210
      3812/4742.5160/44933.60.5660.309–1.0353812/4292.8264/87433.00.7380.408–1.334
      39125/21975.7190/55853.41.3201.006–1.73339204/36775.6404/11,8933.41.2911.065–1.564
      4046/9125.0133/40883.31.2200.832–1.7914058/9596.1277/77503.61.4761.077–2.023
      Cesarean delivery
      WkMultiparous and unfavorableWkMultiparous and favorable
      eIOLExpaOR95% CIeIOLExpaOR95% CI
      No.%No.%No.%No.%
      372/852.4216/24378.90.2830.068–1.173370/640.086/38502.2
      3823/4744.9399/44938.90.4860.313–0.755384/4290.9185/87432.10.4720.173–1.290
      3966/21973.0476/55858.50.3710.279–0.4943927/36770.7339/11,8932.90.4370.288–0.664
      4046/9125.0455/408811.10.4780.343–0.6644016/9591.7279/77503.60.6640.392–1.123
      aOR is of the outcome compared to vaginal delivery for eIOL with expectant as the referent controlling for maternal age, race/ethnicity, body mass index at delivery, insurance, and type of hospital.
      aOR, adjusted odds ratio; CI, confidence interval; eIOL, elective induction of labor; exp, expectant management.
      Gibson. Outcomes in electively induced low-risk term pregnancies. Am J Obstet Gynecol 2014.
      Supplemental Table 2Secondary maternal outcomes by week of elective induction of labor compared to those expectantly managed within the same week of delivery divided by parity
      NulliparousMaternal bleeding complications
      WkeIOLExpaOR95% CI
      No.%No.%
      371/651.5332/40928.10.1960.027–1.424
      3812/3683.3621/86477.20.4810.266–0.867
      39119/14018.5938/13,2797.10.9900.808–1.213
      40127/15698.1856/11,8717.20.8270.674–1.013
      WkMaternal intensive care admission or death
      eIOLExpaOR95% CI
      No.%No.%
      370/720.019/44320.4
      380/3990.028/92120.3
      390/1.5660.024/13,9510.2
      404/20600.230/12,4160.20.8030.271–2.378
      WkMaternal infections
      eIOLExpaOR95% CI
      No.%No.%
      374/685.9545/451412.10.4360.157–1.211
      3823/3826.01246/948713.10.4400.286–0.677
      3997/15406.32198/14,72514.90.4660.377–0.577
      40152/18818.12347/13,36317.60.4950.415–0.590
      WkThird- or fourth-degree perineal or sulcal lacerations
      eIOLExpaOR95% CI
      No.%No.%
      375/726.9433/55217.81.0010.399–2.511
      3835/4048.71174/11,8099.91.0140.709–1.450
      39173/157611.01922/18,38910.51.0290.869–1.218
      40235/212411.11877/17,03411.00.9970.858–1.157
      WkShoulder dystocia
      eIOLExpaOR95% CI
      No.%No.%
      370/720.043/53150.8
      382/4040.5115/11,4041.00.4120.100–1.693
      3927/15761.7212/17,6931.21.4720.973–2.226
      4029/21241.4217/16,2811.31.0800.722–1.616
      MultiparousMaternal bleeding complications
      WkeIOLExpaOR95% CI
      No.%No.%
      379/1326.8459/51518.90.7300.365–1.459
      3851/8226.2836/10,6557.90.6640.493–0.895
      39597/556810.7983/13,7777.11.0240.911–1.152
      40121/15717.7516/91165.70.9670.772–1.211
      WkMaternal intensive care admission or death
      eIOLExpaOR95% CI
      No.%No.%
      371/1490.422/55730.41.8270.221–15.128
      381/9320.132/11,2940.30.7510.098–5.776
      399/59710.249/14,3510.31.0090.442–2.305
      401/19350.133/89140.40.2950.039–2.210
      WkMaternal infections
      eIOLExpaOR95% CI
      No.%No.%
      371/1410.7205/55363.70.1910.026–1.374
      385/8830.6345/11,5593.00.1860.076–0.454
      3947/58640.8532/15,2533.50.3290.240–0.451
      4032/17981.8449/10,2064.40.5310.365–0.772
      WkThird- or fourth-degree perineal or sulcal lacerations
      eIOLExpaOR95% CI
      No.%No.%
      375/1523.3158/67252.41.6760.672–4.179
      3821/9402.2380/14,2962.70.9880.629–1.553
      39116/59871.9569/19,0183.00.7290.584–0.911
      4043/19872.2422/13,1172.20.6670.479–0.929
      WkShoulder dystocia
      eIOLExpaOR95% CI
      No.%No.%
      370/1520.043/64590.7
      388/9400.9198/13,6561.50.6150.300–1.264
      39114/59871.9345/18,0881.91.2060.951–1.531
      4048/19872.4278/12,3622.31.1900.856–1.653
      aOR, adjusted odds ratio; CI, confidence interval; eIOL, elective induction of labor; exp, expectant management.
      aOR is of the outcome compared to vaginal delivery for eIOL with expectant as the referent controlling for maternal age, race/ethnicity, body mass index at delivery, insurance, type of hospital, and modified Bishop score.
      Gibson. Outcomes in electively induced low-risk term pregnancies. Am J Obstet Gynecol 2014.
      Supplemental Table 3Secondary neonatal outcomes by week of elective induction of labor compared to those expectantly managed within the same week of delivery divided by parity
      NulliparousNeonatal complication composite
      WkeIOLExpaOR95% CI
      No.%No.%
      375/726.9619/552111.20.5280.210–1.325
      3816/4044.0968/11,8098.20.4360.262–0.724
      39109/15766.91489/18,3898.10.8370.682–1.028
      40137/21246.51571/17,0349.20.6660.553–0.802
      WkNeonatal respiratory complications
      eIOLExpaOR95% CI
      No.%No.%
      371/721.4240/51274.70.2460.034–1.788
      387/3981.8325/10,9473.00.5260.245–1.130
      3930/15531.9574/17,0493.40.5610.385–0.816
      4046/19632.3552/15,7123.50.6110.447–0.835
      WkPerinatal death
      eIOLExpaOR95% CI
      No.%No.%
      370/720.037/53150.7
      380/4040.044/11,4040.4
      392/15760.168/17,6930.40.3030.074–1.246
      406/21240.365/16,2810.40.5070.214–1.198
      MultiparousNeonatal complication composite
      WkeIOLExpaOR95% CI
      No.%No.%
      379/1525.9609/67259.10.6120.309–1.210
      3844/9404.7863/14,2956.00.7550.551–1.034
      39179/59873.01046/19,0185.50.5080.427–0.604
      4075/19873.8681/13,1175.20.6500.503–0.840
      WkNeonatal respiratory complications
      eIOLExpaOR95% CI
      No.%No.%
      378/1455.5284/61911.61.1530.556–2.392
      3814/8981.6296/13,0802.30.6370.368–1.102
      3960/58841.0372/17,3852.10.4710.350–0.632
      4027/18691.5245/11,9802.10.7390.484–1.127
      WkPerinatal death
      eIOLExpaOR95% CI
      No.%No.%
      370/1520.061/64590.9
      380/9400.073/13,6560.5
      3911/59870.254/18,0880.30.5570.274–1.130
      403/19870.240/12,3620.30.3850.113–1.314
      aOR is of the outcome compared to vaginal delivery for eIOL with expectant as the referent controlling for maternal age, race/ethnicity, body mass index at delivery, insurance, type of hospital, and modified Bishop score.
      aOR, adjusted odds ratio; CI, confidence interval; eIOL, elective induction of labor; exp, expectant management.
      Gibson. Outcomes in electively induced low-risk term pregnancies. Am J Obstet Gynecol 2014.

      References

        • Yeast J.D.
        • Jones A.
        • Poskin M.
        Induction of labor and the relationship to cesarean delivery: a review of 7001 consecutive inductions.
        Am J Obstet Gynecol. 1999; 180: 628-633
        • Smith K.M.
        • Hoffman M.K.
        • Sciscione A.
        Elective induction of labor in nulliparous women increases the risk of cesarean delivery.
        Obstet Gynecol. 2003; 101: 45S
        • Hoffman M.K.
        • Vahratian A.
        • Sciscione A.C.
        • Troendle J.F.
        • Zhang J.
        Comparison of labor progression between induced and noninduced multiparous women.
        Obstet Gynecol. 2006; 107: 1029-1034
        • Glantz J.C.
        Elective induction vs spontaneous labor: associations and outcomes.
        J Reprod Med. 2005; 50: 235-240
        • Caughey A.B.
        • Nicholson J.M.
        • Cheng Y.W.
        • Lyell D.J.
        • Washington A.E.
        Induction of labor and cesarean delivery by gestational age.
        Am J Obstet Gynecol. 2006; 195: 700-705
      1. The National Institute of Child Health and Human Development Network of Maternal-Fetal Medicine Units. A clinical trial of induction of labor versus expectant management in postterm pregnancy. Am J Obstet Gynecol 1994;170:716-23.

        • Cole R.A.
        • Howie P.W.
        • Macnaughton M.C.
        Elective induction of labor: randomized prospective trial.
        Lancet. 1975; 1: 767-770
        • Hannah M.E.
        • Hannah W.J.
        • Hellmann J.
        • Hewson S.
        • Milner R.
        • Willan A.
        Induction of labor as compared with serial antenatal monitoring in post-term pregnancy: a randomized controlled trial; the Canadian Multicenter Post-term Pregnancy Trial Group.
        N Engl J Med. 1992; 326: 1587-1592
        • Caughey A.B.
        • Sundaram V.
        • Kaimal A.J.
        • et al.
        Systematic review: elective induction of labor versus expectant management of pregnancy.
        Ann Intern Med. 2009; 151 (W53-63): 252-263
        • Koopmans C.M.
        • Bijlenga D.
        • Groen H.
        • et al.
        • HYPITAT Study Group
        Induction of labor versus expectant monitoring for gestational hypertension or mild pre-eclampsia after 36 weeks' gestation (HYPITAT): a multicenter, open-label randomized controlled trial.
        Lancet. 2009; 374: 979-988
        • Boers K.E.
        • Vijgen S.M.
        • Bijlenga D.
        • et al.
        • DIGITAT Study Group
        Induction versus expectant monitoring for intrauterine growth restriction at term: randomized equivalence trial (DIGITAT).
        BMJ. 2010; 341: c7087
        • Kjos S.L.
        • Henry O.A.
        • Montoro M.
        Insulin-requiring diabetes in pregnancy: a randomized trial of active induction of labor and expectant management.
        Am J Obstet Gynecol. 1993; 169: 611-615
        • Rayburn W.F.
        • Sokkary N.
        • Clokey D.E.
        Consequences of routine delivery at 38 weeks for A-2 gestational diabetes.
        J Matern Fetal Neonatal Med. 2005; 18: 333-337
        • Stock S.J.
        • Ferguson E.
        • Duffy A.
        • Ford I.
        • Chalmers J.
        • Norman J.E.
        Outcomes of elective induction of labor compared with expectant management: population based study.
        BMJ. 2012; 344: e2838
        • Cheng Y.W.
        • Kaimal A.J.
        • Snowden J.M.
        • Nicholson J.M.
        • Caughey A.B.
        Induction of labor compared to expectant management in low-risk women and associated perinatal outcomes.
        Am J Obstet Gynecol. 2012; 207: 502.e1-502.e8
        • Darney B.G.
        • Snowden J.M.
        • Cheng Y.W.
        • et al.
        Elective induction of labor at term compared with expectant management: maternal and neonatal outcomes.
        Obstet Gynecol. 2013; 122: 761-769
        • Osmundson S.
        • Ou-Yang R.J.
        • Grobman W.A.
        Elective induction compared with expectant management in nulliparous women with an unfavorable cervix.
        Obstet Gynecol. 2011; 117: 583-587
        • Osmundson S.
        • Ou-Yang R.J.
        • Grobman W.A.
        Elective induction compared with expectant management in nulliparous women with a favorable cervix.
        Obstet Gynecol. 2010; 116: 601-605
        • Consortium on Safe Labor
        • Hibbard J.U.
        • Wilkins I.
        • Sun L.
        • et al.
        Respiratory morbidity in late preterm births.
        JAMA. 2010; 304: 419-425
        • Tita A.T.
        • Landon M.B.
        • Spong C.Y.
        • et al.
        Timing of elective repeat cesarean delivery at term and neonatal outcomes; Eunice Kennedy Shriver NICHD Maternal-Fetal Medicine Units Network.
        N Engl J Med. 2009; 360: 111-120
        • Reddy U.M.
        • Ko C.W.
        • Raju T.N.
        • Willinger M.
        Delivery indications at late-preterm gestations and infant mortality rates in the United States.
        Pediatrics. 2009; 124: 234-240
        • Zhang J.
        • Troendle J.
        • Reddy U.M.
        • et al.
        Contemporary cesarean delivery practice in the United States.
        Am J Obstet Gynecol. 2010; 203: 326.e1-326.e10
        • Martin J.A.
        • Hamilton B.E.
        • Sutton P.D.
        • Ventura S.J.
        • Menacker F.
        • Kirmeyer S.
        Births: final data for 2004.
        Natl Vital Stat Rep. 2006; 55: 1-101
        • Laughon S.K.
        • Zhang J.
        • Grewal J.
        • et al.
        Induction of labor in a contemporary obstetric cohort.
        Am J Obstet Gynecol. 2012; 206: 486.e1-486.e9