If you don't remember your password, you can reset it by entering your email address and clicking the Reset Password button. You will then receive an email that contains a secure link for resetting your password
If the address matches a valid account an email will be sent to __email__ with instructions for resetting your password
Reprints: Kelly S. Gibson, MD, Division of Maternal Fetal Medicine, Department of Obstetrics and Gynecology, MetroHealth Medical Center, 2500 MetroHealth Dr., Cleveland, OH 44109.
Division of Maternal Fetal Medicine, Department of Obstetrics and Gynecology, MetroHealth Medical Center–Case Western Reserve University, Cleveland, OH
Division of Maternal Fetal Medicine, Department of Obstetrics and Gynecology, MetroHealth Medical Center–Case Western Reserve University, Cleveland, OH
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.
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.
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.
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.
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.
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.
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.
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
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
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.
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,
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.
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.
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.
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.
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.
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.
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
Variable
Total (131,243)
Nulliparous (64,376)
Parous (66,867)
No.
%
No.
%
No.
%
Maternal age, y
≤19
14,012
10.7
12,270
19.1
1742
2.6
20-34
100,875
76.9
47,122
73.2
53,753
80.4
≥35
16,193
12.3
4917
7.6
11,276
16.9
Missing
163
0.1
67
0.1
96
0.1
Race/ethnicity
African American
26,263
20.0
13,050
20.3
13,213
19.8
Caucasian
67,885
51.7
32,612
50.7
35,273
52.8
Hispanic
22,080
16.8
10,325
16.0
11,755
17.6
Asian
5718
4.4
3406
5.3
2312
3.5
Other
9297
7.1
4983
7.7
4314
6.5
BMI at delivery, kg/m2
Normal/underweight (<25.0)
16,330
12.4
8543
13.3
7787
11.6
Overweight (25.0-29.9)
43,735
33.3
21,972
34.1
21,763
32.5
Obese (30.0-34.9)
28,590
21.8
13,500
21.0
15,090
22.6
Morbid obesity (>35.0)
18,972
14.5
8815
13.7
10,157
15.2
Missing
23,616
18.0
11,546
17.9
12,070
18.0
Insurance
Private
75,200
57.3
36,491
56.7
38,709
57.9
Public
38,732
29.5
19,056
29.6
19,676
29.4
Self-pay
1517
1.2
750
1.2
767
1.1
Other/missing
15,794
12.0
8079
12.6
7715
11.5
Hospital type
University teaching
52,769
40.2
27,763
43.1
25,006
37.4
Community teaching
66,605
50.8
31,943
49.6
34,662
51.8
Community nonteaching
11,869
9.0
4670
7.3
7199
10.8
Modified Bishop score
≤4
55,311
42.1
27,930
43.4
27,381
41.0
>4
75,932
57.9
36,446
56.6
39,486
59.0
Gestational age at delivery, wk
37
12,470
9.5
5593
8.7
6877
10.3
38
27,449
20.9
12,213
19.0
15,236
22.8
39
44,970
34.3
19,965
31.0
25,005
37.4
40
34,262
26.1
19,158
29.8
15,104
22.6
41
12,092
9.2
7447
11.6
4645
6.9
Elective induction, wk
37
224
0.2
72
0.1
152
0.2
38
1344
1.0
404
0.6
940
1.4
39
7563
5.8
1576
2.5
5987
9.0
40
4111
3.1
2124
3.3
1987
3.0
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
Wk
Nulliparous and unfavorable
Wk
Nulliparous and favorable
eIOL
Exp
aOR
95% CI
eIOL
Exp
aOR
95% CI
No.
%
No.
%
No.
%
No.
%
37
33/43
76.7
12,381/21,520
57.5
–
–
37
24/28
85.7
24,503/33,486
73.2
–
–
38
190/285
66.7
9597/17,099
56.1
–
–
38
89/110
80.9
18,986/26,352
71.7
–
–
39
420/602
69.8
5524/10,404
53.1
–
–
39
720/955
75.4
9830/14,201
69.2
–
–
40
629/1094
57.5
1759/3509
50.1
–
–
40
634/917
69.1
2205/3292
67.0
–
–
Operative vaginal delivery
Wk
Nulliparous and unfavorable
Wk
Nulliparous and favorable
eIOL
Exp
aOR
95% CI
eIOL
Exp
aOR
95% CI
No.
%
No.
%
No.
%
No.
%
37
2/43
4.7
1786/21,520
8.3
0.444
0.106–1.861
37
3/28
10.7
4040/33,486
12.1
0.809
0.242–2.707
38
14/285
4.9
1449/17,099
8.5
0.493
0.285–0.854
38
12/110
10.9
3224/26,352
12.2
0.769
0.418–1.412
39
40/602
6.6
876/10,404
8.4
0.522
0.373–0.732
39
157/955
16.4
1756/14,201
12.4
1.011
0.841–1.215
40
112/1094
10.2
268/3509
7.6
0.865
0.669–1.120
40
167/917
18.2
392/3292
11.9
1.144
0.919–1.424
Cesarean delivery
Wk
Nulliparous and unfavorable
Wk
Nulliparous and favorable
eIOL
Exp
aOR
95% CI
eIOL
Exp
aOR
95% CI
No.
%
No.
%
No.
%
No.
%
37
8/43
18.6
7353/21,520
34.2
0.402
0.183–0.884
37
1/28
3.6
4943/33,486
14.8
0.164
0.022–1.228
38
81/285
28.4
6053/17,099
35.4
0.647
0.494–0.847
38
9/110
8.2
4142/26,352
15.7
0.430
0.213–0.864
39
142/602
23.6
4004/10,404
38.5
0.466
0.381–0.569
39
78/955
8.2
2615/14,201
18.4
0.497
0.389–0.633
40
353/1094
32.3
1482/3509
42.3
0.689
0.588–0.807
40
116/917
12.7
695/3292
21.1
0.694
0.551–0.874
Multiparous
Nonoperative vaginal delivery
Wk
Multiparous and unfavorable
Wk
Multiparous and favorable
eIOL
Exp
aOR
95% CI
eIOL
Exp
aOR
95% CI
No.
%
No.
%
No.
%
No.
%
37
83/85
97.7
17,334/19,782
87.6
–
–
37
62/64
96.9
33,345/35,572
93.7
–
–
38
439/474
92.6
12,961/14,815
87.5
–
–
38
413/429
96.3
24,638/26,400
93.3
–
–
39
2006/2197
61.3
6036/7033
85.8
–
–
39
3446/3677
93.7
10,042/10,830
92.7
–
–
40
820/912
89.9
1716/2033
84.4
–
–
40
885/959
92.3
1963/2121
92.6
–
–
Operative vaginal delivery
Wk
Multiparous and unfavorable
Wk
Multiparous and favorable
eIOL
Exp
aOR
95% CI
eIOL
Exp
aOR
95% CI
No.
%
No.
%
No.
%
No.
%
37
0/85
0.0
733/19,782
3.7
–
–
37
2/64
3.1
1286/35,572
3.6
0.788
0.192–3.238
38
12/474
2.5
561/14,815
3.8
0.550
0.307–0.985
38
12/429
2.8
1010/26,400
3.8
0.610
0.342–1.089
39
125/2197
5.7
246/7033
3.5
1.139
0.879–1.477
39
204/3677
5.6
402/10,830
3.7
1.242
1.017–1.516
40
46/912
5.0
67/2033
3.3
1.091
0.701–1.698
40
58/959
6.1
67/2121
3.2
1.694
1.123–2.555
Cesarean delivery
Wk
Multiparous and unfavorable
Wk
Multiparous and favorable
eIOL
Exp
aOR
95% CI
eIOL
Exp
aOR
95% CI
No.
%
No.
%
No.
%
No.
%
37
2/85
2.4
1715/19,782
8.7
0.265
0.064–1.088
37
0/64
0.0
941/35,572
2.7
–
–
38
23/474
4.9
1293/14,815
8.7
0.553
0.360–0.850
38
4/429
0.9
752/26,400
2.9
0.421
0.156–1.137
39
66/2197
3.0
751/7033
10.7
0.346
0.262–0.456
39
27/3677
0.7
386/10,830
3.6
0.352
0.231–0.534
40
46/912
5.0
250/2033
12.3
0.437
0.307–0.622
40
16/959
1.7
91/2121+A48
4.3
0.536
0.297–0.968
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.
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
Nulliparous
Maternal bleeding complications
Wk
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
1/65
1.5
2990/42,230
7.1
0.211
0.029–1.521
38
12/368
3.3
2357/33,215
7.1
0.414
0.232–0.740
39
119/1401
8.5
1300/18,535
7.0
1.010
0.827–1.233
40
127/1569
8.1
317/5095
6.2
0.987
0.784–1.243
Wk
Maternal intensive care admission or death
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
0/72
0.0
97/44,728
0.2
–
–
38
0/399
0.0
69/35,117
0.2
–
–
39
0/1.566
0.0
45/19,600
0.2
–
–
40
4/2060
0.2
11/5124
0.2
0.984
0.273–3.552
Wk
Maternal infections
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
4/68
5.9
7155/46,978
15.2
0.345
0.125–0.952
38
23/382
6.0
5886/37,109
15.9
0.347
0.227–0.530
39
97/1540
6.3
3591/20,844
17.2
0.405
0.328–0.500
40
152/1881
8.1
1092/5600
19.5
0.454
0.377–0.546
Wk
Third- or fourth-degree perineal or sulcal lacerations
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
5/72
6.9
6206/58,783
10.6
0.767
0.308–1.910
38
35/404
8.7
4997/46,570
10.7
0.969
0.683–1.377
39
173/1576
11.0
2902/26,605
10.9
0.896
0.759–1.057
40
235/2124
11.1
790/7447
10.6
0.978
0.829–1.153
Wk
Shoulder dystocia
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
0/72
0.0
697/56,479
1.2
–
–
38
2/404
0.5
580/44,671
1.3
0.357
0.088–1.439
39
27/1576
1.7
341/25,402
1.3
1.292
0.865–1.929
40
29/2124
1.4
95/6997
1.4
1.134
0.732–1.757
Multiparous
Maternal bleeding complications
Wk
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
9/132
6.8
3269/44,661
7.3
0.896
0.453–1.772
38
51/822
6.2
2382/33,184
7.2
0.703
0.526–0.939
39
597/5568
10.7
802/13,839
5.8
1.360
1.199–1.542
40
121/1571
7.7
165/3152
5.2
1.069
0.810–1.412
Wk
Maternal intensive care admission or death
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
1/149
0.4
140/46,345
0.3
3.596
0.482–26.832
38
1/932
0.1
107/34,119
0.3
0.755
0.104–5.498
39
9/5971
0.2
49/13,797
0.4
1.602
0.679–3.779
40
1/1935
0.1
15/2948
0.5
0.402
0.050–3.206
Wk
Maternal infections
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
1/141
0.7
1561/49,079
3.2
0.214
0.030–1.536
38
5/883
0.6
1211/36,637
3.3
0.196
0.081–0.475
39
47/5864
0.8
632/15,520
4.1
0.340
0.248–0.466
40
32/1798
1.8
151/3516
4.3
0.717
0.474–1.083
Wk
Third- or fourth-degree perineal or sulcal lacerations
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
5/152
3.3
1687/59,990
2.8
1.279
0.523–3.129
38
21/940
2.2
1286/44,754
2.9
0.846
0.546–1.312
39
116/5987
1.9
601/19,749
3.0
0.612
0.491–0.764
40
43/1987
2.2
136/4645
2.9
0.669
0.457–0.977
Wk
Shoulder dystocia
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
0/152
0.0
1084/57,306
1.9
–
–
–
38
8/940
0.9
878/42,710
2.1
0.424
0.211
0.856
39
114/5987
1.9
419/18,635
2.3
0.981
0.776
1.240
40
48/1987
2.4
93/4286
2.2
1.194
0.809
1.761
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.
Table 4Secondary outcomes of neonatal morbidity by week of elective induction of labor compared to those expectantly managed divided by parity
Nulliparous
Neonatal complication composite
Wk
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
5/72
6.9
5033/58,783
8.6
0.782
0.314–1.947
38
16/404
4.0
4049/46,570
8.7
0.433
0.262–0.716
39
109/1576
6.9
2451/26,605
9.2
0.750
0.613–0.917
40
137/2124
6.5
743/7447
10.0
0.652
0.535–0.795
Wk
Neonatal respiratory complications
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
1/72
1.4
1799/54,455
3.3
0.371
0.051–2.674
38
7/398
1.8
1467/43,110
3.4
0.465
0.219–0.986
39
30/1553
1.9
863/24,508
3.5
0.540
0.373–0.783
40
46/1963
2.3
265/6833
0.9
0.589
0.423–0.821
Wk
Perinatal death
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
0/72
0.0
202/56,479
0.4
–
–
38
0/404
0.0
158/44,671
0.4
–
–
39
2/1576
0.1
88/25,402
0.4
0.348
0.085–1.424
40
6/2124
0.3
17/6997
0.2
1.091
0.398–2.992
Multiparous
Neonatal complication composite
Wk
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
9/152
5.9
3120/59,990
5.2
1.197
0.608–2.354
38
44/940
4.7
2213/44,754
4.9
0.981
0.721–1.334
39
179/5987
3.0
988/19,749
5.0
0.590
0.494–0.705
40
75/1987
3.8
232/4645
5.0
0.756
0.564–1.012
Wk
Neonatal respiratory complications
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
8/145
5.5
1107/55,284
2.0
2.897
1.412–5.945
38
14/898
1.6
797/41,306
1.9
0.827
0.484–1.413
39
60/5884
1.0
365/18,037
2.0
0.574
0.424–0.778
40
27/1869
1.5
93/4198
2.2
0.685
0.424–1.109
Wk
Perinatal death
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
0/152
0.0
195/57,306
0.3
–
–
38
0/940
0.0
122/42,710
0.3
–
–
39
11/5987
0.2
57/18,635
0.3
0.781
0.376–1.625
40
3/1987
0.2
14/4286
0.3
0.630
0.163–2.429
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.
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.
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
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.
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.
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.
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
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.
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
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
Wk
Nulliparous and unfavorable
Wk
Nulliparous and favorable
eIOL
Exp
aOR
95% CI
eIOL
Exp
aOR
95% CI
No.
%
No.
%
No.
%
No.
%
37
33/43
76.7
1502/3288
65.7
–
–
37
24/28
85.7
2366/2932
80.7
–
–
38
190/285
66.7
2594/4136
62.7
–
–
38
89/110
80.9
5428/7024
77.3
–
–
39
420/602
69.8
3653/6093
60.0
–
–
39
720/955
75.4
8436/11,196
75.4
–
–
40
629/1094
57.5
3136/5801
54.1
–
–
40
634/917
69.1
6991/9992
70.0
–
–
Operative vaginal delivery
Wk
Nulliparous and unfavorable
Wk
Nulliparous and favorable
eIOL
Exp
aOR
95% CI
eIOL
Exp
aOR
95% CI
No.
%
No.
%
No.
%
No.
%
37
2/43
4.7
161/2288
7.0
0.562
0.132–2.402
37
3/28
10.7
324/2932
11.1
0.978
0.290–3.301
38
14/285
4.9
323/4136
7.8
0.531
0.302–0.931
38
12/110
10.9
804/7024
11.5
0.863
0.468–1.594
39
40/602
6.6
533/6093
8.8
0.583
0.414–0.821
39
157/955
16.4
1311/11,196
11.7
1.209
1.002–1.458
40
112/1094
10.2
496/5801
8.6
0.830
0.655–1.050
40
167/917
18.2
1197/9992
12.0
1.215
1.006–1.467
Cesarean delivery
Wk
Nulliparous and unfavorable
Wk
Nulliparous and favorable
eIOL
Exp
aOR
95% CI
eIOL
Exp
aOR
95% CI
No.
%
No.
%
No.
%
No.
%
37
8/43
18.6
625/2288
27.3
0.558
0.250–1.241
37
1/28
3.6
242/2932
8.3
0.327
0.043–2.459
38
81/285
28.4
1219/4136
29.5
0.848
0.641–1.122
38
9/110
8.2
792/7024
11.3
0.593
0.293–1.200
39
142/602
23.6
1907/6093
31.3
0.632
0.514–0.776
39
78/955
8.2
1449/11,196
12.9
0.735
0.574–0.942
40
353/1094
32.3
2169/5801
37.4
0.844
0.727–0.981
40
116/917
12.7
1804/9992
18.0
0.858
0.694–1.062
Multiparous
Nonoperative vaginal delivery
Wk
Multiparous and unfavorable
Wk
Multiparous and favorable
eIOL
Exp
aOR
95% CI
eIOL
Exp
aOR
95% CI
No.
%
No.
%
No.
%
No.
%
37
83/85
97.7
2142/2437
87.9
–
–
37
62/64
96.9
3660/3850
95.1
–
–
38
439/474
92.6
3934/4493
87.6
–
–
38
413/429
96.3
8294/8743
94.9
–
–
39
2006/2197
61.3
4919/5585
88.1
–
–
39
3446/3677
93.7
11,150/11,893
93.8
–
–
40
820/912
89.9
3500/4088
85.6
–
–
40
885/959
92.3
7194/7750
92.8
–
–
Operative vaginal delivery
Wk
Multiparous and unfavorable
Wk
Multiparous and favorable
eIOL
Exp
aOR
95% CI
eIOL
Exp
aOR
95% CI
No.
%
No.
%
No.
%
No.
%
37
0/85
0.0
79/2437
3.2
–
–
37
2/64
3.1
104/3850
2.7
1.012
0.243–4.210
38
12/474
2.5
160/4493
3.6
0.566
0.309–1.035
38
12/429
2.8
264/8743
3.0
0.738
0.408–1.334
39
125/2197
5.7
190/5585
3.4
1.320
1.006–1.733
39
204/3677
5.6
404/11,893
3.4
1.291
1.065–1.564
40
46/912
5.0
133/4088
3.3
1.220
0.832–1.791
40
58/959
6.1
277/7750
3.6
1.476
1.077–2.023
Cesarean delivery
Wk
Multiparous and unfavorable
Wk
Multiparous and favorable
eIOL
Exp
aOR
95% CI
eIOL
Exp
aOR
95% CI
No.
%
No.
%
No.
%
No.
%
37
2/85
2.4
216/2437
8.9
0.283
0.068–1.173
37
0/64
0.0
86/3850
2.2
–
–
38
23/474
4.9
399/4493
8.9
0.486
0.313–0.755
38
4/429
0.9
185/8743
2.1
0.472
0.173–1.290
39
66/2197
3.0
476/5585
8.5
0.371
0.279–0.494
39
27/3677
0.7
339/11,893
2.9
0.437
0.288–0.664
40
46/912
5.0
455/4088
11.1
0.478
0.343–0.664
40
16/959
1.7
279/7750
3.6
0.664
0.392–1.123
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.
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
Nulliparous
Maternal bleeding complications
Wk
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
1/65
1.5
332/4092
8.1
0.196
0.027–1.424
38
12/368
3.3
621/8647
7.2
0.481
0.266–0.867
39
119/1401
8.5
938/13,279
7.1
0.990
0.808–1.213
40
127/1569
8.1
856/11,871
7.2
0.827
0.674–1.013
Wk
Maternal intensive care admission or death
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
0/72
0.0
19/4432
0.4
–
–
38
0/399
0.0
28/9212
0.3
–
–
39
0/1.566
0.0
24/13,951
0.2
–
–
40
4/2060
0.2
30/12,416
0.2
0.803
0.271–2.378
Wk
Maternal infections
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
4/68
5.9
545/4514
12.1
0.436
0.157–1.211
38
23/382
6.0
1246/9487
13.1
0.440
0.286–0.677
39
97/1540
6.3
2198/14,725
14.9
0.466
0.377–0.577
40
152/1881
8.1
2347/13,363
17.6
0.495
0.415–0.590
Wk
Third- or fourth-degree perineal or sulcal lacerations
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
5/72
6.9
433/5521
7.8
1.001
0.399–2.511
38
35/404
8.7
1174/11,809
9.9
1.014
0.709–1.450
39
173/1576
11.0
1922/18,389
10.5
1.029
0.869–1.218
40
235/2124
11.1
1877/17,034
11.0
0.997
0.858–1.157
Wk
Shoulder dystocia
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
0/72
0.0
43/5315
0.8
–
–
38
2/404
0.5
115/11,404
1.0
0.412
0.100–1.693
39
27/1576
1.7
212/17,693
1.2
1.472
0.973–2.226
40
29/2124
1.4
217/16,281
1.3
1.080
0.722–1.616
Multiparous
Maternal bleeding complications
Wk
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
9/132
6.8
459/5151
8.9
0.730
0.365–1.459
38
51/822
6.2
836/10,655
7.9
0.664
0.493–0.895
39
597/5568
10.7
983/13,777
7.1
1.024
0.911–1.152
40
121/1571
7.7
516/9116
5.7
0.967
0.772–1.211
Wk
Maternal intensive care admission or death
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
1/149
0.4
22/5573
0.4
1.827
0.221–15.128
38
1/932
0.1
32/11,294
0.3
0.751
0.098–5.776
39
9/5971
0.2
49/14,351
0.3
1.009
0.442–2.305
40
1/1935
0.1
33/8914
0.4
0.295
0.039–2.210
Wk
Maternal infections
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
1/141
0.7
205/5536
3.7
0.191
0.026–1.374
38
5/883
0.6
345/11,559
3.0
0.186
0.076–0.454
39
47/5864
0.8
532/15,253
3.5
0.329
0.240–0.451
40
32/1798
1.8
449/10,206
4.4
0.531
0.365–0.772
Wk
Third- or fourth-degree perineal or sulcal lacerations
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
Nulliparous
Neonatal complication composite
Wk
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
5/72
6.9
619/5521
11.2
0.528
0.210–1.325
38
16/404
4.0
968/11,809
8.2
0.436
0.262–0.724
39
109/1576
6.9
1489/18,389
8.1
0.837
0.682–1.028
40
137/2124
6.5
1571/17,034
9.2
0.666
0.553–0.802
Wk
Neonatal respiratory complications
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
1/72
1.4
240/5127
4.7
0.246
0.034–1.788
38
7/398
1.8
325/10,947
3.0
0.526
0.245–1.130
39
30/1553
1.9
574/17,049
3.4
0.561
0.385–0.816
40
46/1963
2.3
552/15,712
3.5
0.611
0.447–0.835
Wk
Perinatal death
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
0/72
0.0
37/5315
0.7
–
–
38
0/404
0.0
44/11,404
0.4
–
–
39
2/1576
0.1
68/17,693
0.4
0.303
0.074–1.246
40
6/2124
0.3
65/16,281
0.4
0.507
0.214–1.198
Multiparous
Neonatal complication composite
Wk
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
9/152
5.9
609/6725
9.1
0.612
0.309–1.210
38
44/940
4.7
863/14,295
6.0
0.755
0.551–1.034
39
179/5987
3.0
1046/19,018
5.5
0.508
0.427–0.604
40
75/1987
3.8
681/13,117
5.2
0.650
0.503–0.840
Wk
Neonatal respiratory complications
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
8/145
5.5
284/6191
1.6
1.153
0.556–2.392
38
14/898
1.6
296/13,080
2.3
0.637
0.368–1.102
39
60/5884
1.0
372/17,385
2.1
0.471
0.350–0.632
40
27/1869
1.5
245/11,980
2.1
0.739
0.484–1.127
Wk
Perinatal death
eIOL
Exp
aOR
95% CI
No.
%
No.
%
37
0/152
0.0
61/6459
0.9
–
–
38
0/940
0.0
73/13,656
0.5
–
–
39
11/5987
0.2
54/18,088
0.3
0.557
0.274–1.130
40
3/1987
0.2
40/12,362
0.3
0.385
0.113–1.314
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.
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.
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.
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.
Cite this article as: Gibson KS, Waters TP, Bailit JL. Maternal and neonatal outcomes in electively induced low-risk term pregnancies. Am J Obstet Gynecol 2014;211:249.e1-16.
00221-X&id=gr1.jpg){kind=link}