Volume 202, Issue 3 , Pages 250.e1-250.e8, March 2010
Neonatal outcome following elective cesarean section beyond 37 weeks of gestation: a 7-year retrospective analysis of a national registry
Article Outline
Objective
We sought to evaluate number and timing of elective cesarean sections at term and to assess perinatal outcome associated with this timing.
Study Design
We conducted a recent retrospective cohort study including all elective cesarean sections of singleton pregnancies at term (n = 20,973) with neonatal follow-up. Primary outcome was defined as a composite of neonatal mortality and morbidity.
Results
More than half of the neonates were born at <39 weeks of gestation, and they were at significantly higher risk for the composite primary outcome than neonates born thereafter. The absolute risks were 20.6% and 12.5% for birth at <38 and 39 weeks, respectively, as compared to 9.5% for neonates born ≥39 weeks. The corresponding adjusted odds ratios (95% confidence interval) were 2.4 (2.1–2.8) and 1.4 (1.2–1.5), respectively.
Conclusion
More than 50% of the elective cesarean sections are applied at <39 weeks, thus jeopardizing neonatal outcome.
Key words: cesarean section, elective, neonatal morbidity, neonatal outcome, timing
In The Netherlands the incidence of a cesarean section has increased from 8.5% in 19931 to 15.1% in 2007.2 The risk for pulmonary disorders and subsequent transfer rates to the neonatal intensive care unit (NICU) are significantly higher after a planned cesarean delivery compared to planned vaginal delivery.3, 4, 5, 6, 7 It is known that, even in term pregnancies, the risk for neonatal respiratory morbidity after a planned cesarean section diminishes significantly with an increase of gestational age until week 39+0.8, 9, 10, 11, 12 Because of the rising incidence of cesarean sections, correct timing of the elective cesarean section is of the utmost importance to prevent unnecessary neonatal (respiratory) morbidity.
See related editorials, pages 207 and 208
For Editors' Commentary, see Table of Contents
Tita et al12 recently showed that neonatal morbidity is still significantly higher in neonates born after an elective repeat cesarean section between 38+4-38+6 weeks as compared to neonates born thereafter. The aims of our study were to evaluate the number and timing of elective cesarean sections at term in The Netherlands and to assess perinatal outcome associated with this timing.
Materials and Methods
The Netherlands Perinatal Registry (PRN) is a national database that includes 96% of all approximately 190,000 deliveries per year at >16 completed weeks of gestation in The Netherlands, which are under supervision of a midwife or an obstetrician.13 After every delivery and after every admitted neonate, standardized digital forms are entered in this nationwide database. The neonatal follow-up in the PRN is registered for around 68% of all hospitals in The Netherlands. All items recorded in the PRN are recorded by the caregiver, who can use a standard manual with additional information on the definitions. The data are annually sent to the national registry office, where a number of range and consistency checks (routine audit) are conducted. False records are sent back to the caregiver, who is given ample opportunity to correct them. In an earlier study, we have compared outcome measures–such as perinatal mortality–in our PRN with civil registration data, and it appeared that the quality of the outcome measurements was high.14
For this study, data from the PRN concerning 1,300,099 births from Jan. 1, 2000, through Dec. 31, 2006, were analyzed for perinatal outcome after elective cesarean section at term. The study was limited to those hospitals that systematically registered neonatal follow-up. In addition, pregnancies complicated by intrauterine fetal deaths, emergency cesarean sections, multiple pregnancies, fetus with congenital anomalies, elective cesarean sections after spontaneous rupture of membranes or signs of labor, and mothers with an adverse medical or obstetric history and/or complications of pregnancy that could influence the risk for neonatal morbidity were excluded. Indications for an elective cesarean section included repeat cesarean section, breech presentation, traumatic first pregnancy, or maternal request.
According to national guidelines,15 calculation of gestational age was based on the first day of the last menstrual period and verified by a first-trimester ultrasound. In case of discrepancy between the 2 measurements (error margin 7 days), gestational age was determined by the results of the first-trimester ultrasound.
Outcome measures
We defined our primary outcome as a composite measure of neonatal mortality until the 28th day after birth, and/or neonatal morbidity, which includes any of the following adverse events: severe resuscitation (defined as endotracheal artificial respiration and/or administration of buffers and/or other), sepsis (including both clinically suspected patients as well as proven infections with positive cultures), respiratory complications (registered as respiratory distress syndrome, wet lung syndrome or transient tachypnea of the newborn, pneumothorax, or air leakage), respiratory support (oxygen, intermittent positive pressure ventilation, continuous positive airway pressure), hypoglycemia (defined as a serum or plasma glucose level of <2.5 mmol/L), neurologic morbidity (described as convulsions or intracranial hemorrhage), admission to the NICU, admission to any neonatal ward ≥5 days, and a 5-minute Apgar score ≤3. In addition to our primary outcome measure we also analyzed the incidence and odds ratio (OR) for any of the above individual outcome measures and for: a 5-minute Apgar score ≤7, necrotizing enterocolitis, meconium aspiration, and hyperbilirubinemia. To be able to compare our results with the literature we also defined a combined respiratory outcome measure, including both respiratory complications (respiratory distress syndrome, transient tachypnea of the newborn, pneumothorax, air leakage) and respiratory support (oxygen, intermittent positive pressure ventilation, continuous positive airway pressure). The follow-up of neonates stopped at discharge from the hospital. If they were transferred to another hospital (eg, a university hospital), follow-up was continued.
Socioeconomic status was based on the mean household income level of the neighborhood, which was determined by the first 4 digits of the woman's postal code. Small for gestational age was defined as a birthweight <10th percentile, derived from sex-, parity- and race-specific growth curves.16
Statistical analysis
We calculated the incidence of neonatal outcomes for each completed week of gestation at the time of cesarean section. The Cochran-Armitage test for trend was used to test the presence of trends. Logistic regression analyses were used to study the association between neonatal outcomes and gestational age at delivery relative to 39 completed weeks of gestation. For each outcome we calculated the OR and 95% confidence interval (CI) and adjusted for potential confounders known to be associated with these outcomes: maternal age,4, 12 ethnicity,12 parity,4 socioeconomic status,4, 12 fetal gender,9, 17 and fetal position.9 The robustness of our findings was tested by performing 4 sensitivity analyses and repeating the regression analyses in which: (1) births with uncertain gestational age (2.6%) were excluded; (2) infants with a birthweight <10th percentile were excluded; (3) infants in nonvertex position were excluded; and (4) additional adjustments for study center were performed to correct for potential variation in clinical decision making. Missing values occurred for only 0.007% of all confounders and were imputed once,18, 19 using R software (The R Foundation, Vienna, Austria).20 All other analyses were performed using SAS software (Version 9.1; SAS Institute, Cary NC).
Results
The Figure shows the study profile. In the study period, 1,300,099 births of single and multiple pregnancies were registered by the PRN. We excluded 12,671 births because of intrauterine fetal deaths or termination of pregnancy. We also excluded 1,094,961 vaginal births, 104,103 emergency cesarean sections, and 1433 births because of missing data. Among 86,931 planned cesarean sections, 49,079 (56.5%) deliveries were registered as elective. Initially we excluded all births at <37+0 weeks of gestation (n = 2122), secondly 4146 multiple pregnancies, thirdly 1076 fetuses with congenital malformations, and subsequently 2910 mothers with an adverse medical or obstetric history and/or complications of pregnancy that could influence the risk of neonatal morbidity. Finally, 17,852 cases were excluded because of incomplete follow-up. We therefore report on 20,973 elective cesarean sections.
FIGURE.
Flowchart
*Hemolysis, elevated liver-enzymes, and low platelet count; †acquired immunodeficiency syndrome; ‡toxoplasmosis, German measles, cytomegalovirus, herpes simplex.
Wilmink. Neonatal outcome following elective cesarean section beyond 37 weeks of gestation. Am J Obstet Gynecol 2010.
A total of 11,873 (56.6%) elective cesarean sections were performed at <39+0 weeks of gestation, 1734 (8.3%) at 37+0-6 weeks, and 10,139 (48.3%) at 38+0-6 weeks. At 39+0-6 weeks of gestation, 6647 (31.7%) elective cesarean sections were performed and 2453 (11.7%) were performed at ≥40+0 weeks (Table 1).
TABLE 1. Maternal and neonatal characteristics shown per week of gestation delivery
| Characteristic | n (%) | n (%) | n (%) | n (%) | n (%) | n (%) |
|---|---|---|---|---|---|---|
| Week of gestation | 37+0–6 | 38+0–6 | 39+0–6 | 40+0–6 | 41+0–6 | ≥42 |
| Proportion of deliveries | n = 1734 (8.3%) | n = 10,139 (48.3%) | n = 6647 (31.7%) | n = 1274 (6.1%) | n = 782 (3.7%) | n = 397 (1.9%) |
| MOTHERS | ||||||
| Age at deliverya | ||||||
 Mean, yb | 32.1±4.6 | 31.9±4.4 | 32.0±4.5 | 31.9±4.7 | 31.7±4.5 | 31.7±4.5 |
| <20 | 17(1.0) | 54(0.5) | 33(0.5) | 3(0.2) | 6(0.8) | 2(0.5) |
| 20 to <25 | 85(4.9) | 482(4.8) | 340(5.1) | 77(6.0) | 37(4.7) | 24(6.1) |
| 25 to <30 | 355(20.5) | 2325(22.9) | 1428(21.5) | 299(23.5) | 195(24.9) | 96(24.2) |
| 30 to <35 | 742(42.8) | 4464(44.0) | 2959(44.5) | 542(42.5) | 341(43.6) | 164(41.3) |
| 35 to <40 | 457(26.4) | 2413(23.8) | 1585(23.9) | 292(22.9) | 172(22.0) | 95(23.9) |
| ≥40 | 78(4.5) | 401(4.0) | 302(4.5) | 61(4.8) | 31(4.0) | 16(4.0) |
| Race or ethnic groupa | ||||||
| Western | 1557(91.5) | 9103(91.7) | 5878(91.2) | 1069(87.2) | 688(89.4) | 342(88.4) |
| Asian | 28(1.7) | 146(1.5) | 109(1.7) | 33(2.7) | 10(1.3) | 3(0.8) |
| Other | 116(6.8) | 677(6.8) | 459(7.1) | 124(8.3) | 72(9.4) | 42(10.9) |
| Paritya | ||||||
| Primiparas | 594(34.3) | 3714(36.6) | 2745(41.3) | 419(32.9) | 295(37.7) | 156(39.3) |
| Multiparas | 1140(65.7) | 6425(63.4) | 3902(58.7) | 855(67.1) | 487(62.3) | 241(60.7) |
| Socioeconomic statusa | ||||||
| Very high | 359(21.0) | 2009(20.2) | 1442(22.0) | 237(18.8) | 153(19.8) | 71(17.9) |
| High | 362(21.2) | 2156(21.7) | 1336(20.4) | 268(21.3) | 184(23.8) | 92(23.2) |
| Normal | 331(19.4) | 1901(19.1) | 1190(18.2) | 224(17.8) | 135(17.5) | 81(20.5) |
| Low | 336(19.7) | 1856(18.6) | 1170(17.9) | 221(17.6) | 128(16.6) | 65(16.4) |
| Very low | 318(18.6) | 2034(20.4) | 1414(21.6) | 308(24.5) | 173(22.4) | 87(22.0) |
| INFANTS | ||||||
| Sexa | ||||||
| Male | 855(49.3) | 4941(48.7) | 3172(47.7) | 663(52.0) | 402(51.4) | 202(50.9) |
| Female | 878(50.7) | 5197(51.3) | 3475(52.3) | 611(48.0) | 380(48.6) | 195(49.1) |
| Positiona | ||||||
| Vertex | 957(55.2) | 4746(46.9) | 2943(44.3) | 754(59.3) | 475(60.9) | 285(71.8) |
| Breech | 688(39.7) | 5029(49.6) | 3434(51.7) | 458(36.0) | 279(35.8) | 99(24.9) |
| Other | 88(5.1) | 355(3.5) | 266(4.0) | 59(4.6) | 26(3.3) | 13(3.3) |
| Birthweighta | ||||||
| Mean - gc | 3183±484 | 3358±459 | 3495±463 | 3739±515 | 3868±512 | 3908±528 |
| <2500 g | 118(6.8) | 208(2.1) | 70(1.1) | 4(0.3) | 0 | 3(0.8) |
| Small for gestational age(<p10)a | 113(6.5) | 581(5.7) | 487(7.3) | 101(7.9) | 61(7.8) | 36(9.0) |
| Large for gestational age(>p90)a | 233(13.4) | 1246(12.3) | 917(13.8) | 250(19.6) | 146(18.7) | 63 (15.9) |
aP value <.05; |
bPlus-minus values are means |
cgrams. |
Maternal and infant characteristics differed among the different categories for gestational age (Table 1). Compared to women who delivered at ≥39+0 weeks, women who delivered at <39+0 weeks of gestation tended to be slightly older, of Western origin, and multiparous. The mean birthweight increased with an increasing gestational age at delivery. Neonates born at ≥39+0 weeks of gestation were significantly more often small (<10th percentile) or large (>90th percentile) for gestational age.
The overall and separate incidence rates of the study outcomes are shown per week of gestation in Table 2. Neonates born at 37+0-6 or 38+0-6 weeks of gestation were, compared to neonates born at ≥39+0 weeks of gestation, at significantly higher risk for the composite primary outcome. The absolute risks were 20.6% at 37+0-6 and 12.5% at 38+0-6 weeks compared with 9.5% at 39+0-6 weeks of gestation (P for trend <.0001). Most separate neonatal outcomes showed significant trends (P for trend < .05) toward an increased incidence for delivery <39+0 weeks (Table 2). During our study period 3 neonates died within 24 hours after delivery (1 each at 37, 39, and 42 weeks of gestation), and 1 neonate died between day 2 and 7 at 38 weeks of gestation.
TABLE 2. Incidence of neonatal morbidity after elective cesarean section per week of gestation delivery
| Outcome | n (%) | n (%) | n (%) | n (%) | n (%) | n (%) | P for trenda |
|---|---|---|---|---|---|---|---|
| Week of gestation | 37+0–6 | 38+0–6 | 39+0–6 | 40+0–6 | 41+0–6 | ≥42 | |
| Proportion of deliveries | (n = 1734) | (n = 10,139) | (n = 6647) | (n = 1274) | (n = 782) | (n = 397) | |
| Primary outcome(including neonatal death)b | 358(20.6) | 1265(12.5) | 634(9.5) | 120(9.4) | 79(10.1) | 39(9.8) | <.0001 |
| Resuscitation | |||||||
| Oxygen | 68(3.9) | 275(2.7) | 161(2.4) | 33(2.6) | 23(2.9) | 9(2.3) | |
| Mask-balloon ventilation | 34(2.0) | 127(1.3) | 70(1.1) | 11(0.9) | 5(0.6) | 1(0.3) | |
| Severe resuscitation | 1(0.1) | 8(0.1) | 6(0.1) | 0 | 0 | 0 | .3349 |
| Sepsis | 14(0.8) | 37(0.4) | 14(0.2) | 5(0.4) | 3(0.4) | 1(0.3) | .0003 |
| Combined respiratory outcomec | 118(6.8) | 356(3.5) | 136(2.1) | 25(2.0) | 14(1.8) | 3(0.8) | <.0001 |
| Respiratory distress syndrome | 8(0.5) | 21(0.2) | 7(0.1) | 0 | 0 | 0 | .0022 |
| Transient tachypnea of the newborn | 72(4.2) | 256(2.5) | 91(1.4) | 19(1.5) | 8(1.0) | 0 | <.0001 |
| Intermittent positive pressure ventilation | 10(0.6) | 15(0.2) | 5(0.1) | 1(0.1) | 1(0.1) | 0 | <.0001 |
| Continuous positive airway pressure | 34(2.0) | 54(0.5) | 15(0.2) | 1(0.1) | 2(0.3) | 0 | <.0001 |
| Hypoglycemia | 56(3.2) | 207(2.0) | 102(1.5) | 25(2.0) | 14(1.8) | 7(1.8) | <.0001 |
| Convulsions | 1(0.1) | 9(0.1) | 3(0.05) | 1(0.1) | 0 | 0 | .2578 |
| Admission | |||||||
| To the neonatal intensive care unit | 13(0.8) | 32(0.3) | 16(0.2) | 2(0.2) | 1(0.1) | 0 | .0031 |
| To any neonatal ward ≥5 days | 214(12.3) | 629(6.2) | 290(4.4) | 51(4.0) | 43(5.5) | 22(5.5) | <.0001 |
| Apgar scored | |||||||
| ≤3 | 1(0.1) | 3(0.03) | 1(0.02) | 0 | 1(0.1) | 0 | .1687 |
| ≤6 | 11(0.6) | 29(0.3) | 11(0.2) | 3(0.2) | 5(0.6) | 0 | .0011 |
| Meconium aspiration | 1(0.1) | 0 | 4(0.1) | 0 | 0 | 0 | .1130 |
| Hyperbilirubinemia | 30(1.7) | 61(0.6) | 35(0.5) | 3(0.2) | 6(0.8) | 1(0.3) | <.0001 |
aThe P value was calculated by the Cochrane-Armitage test for trend for the period from 37 to 39 weeks only; |
bPrimary outcome is defined as a composite measure of neonatal mortality until the 28th day after birth, and/or neonatal morbidity which can consist of any of the following adverse events: severe resuscitation, sepsis, respiratory complications |
cCombined respiratory outcome is defined as a composite measure of: RDS, TTN, pneumothorax, air leakage, oxygen, IPPV and CPAP; |
d5-minute Apgar score. |
The analyses adjusted for potential confounders confirmed the observed trends toward the decreasing incidence of outcome measures with increasing gestational age up to 39+0 weeks of gestation (Table 3). Adjusted ORs (95% CI) for the primary outcome at 37+0-6 and 38+0-6 weeks were 2.4 (2.1–2.8) and 1.4 (1.2–1.5), respectively. When exclusively considering the combined respiratory outcome absolute risks were 6.8% at 37+0-6 weeks and 3.5% at 38+0-6 weeks compared with 2.1% at 39+0-6 weeks of gestation, with ORs (95% CI), at 37+0-6 and 38+0-6 weeks of 3.2 (2.5–4.2) and 1.7 (1.4–2.1), respectively.
TABLE 3. Adjusted odds ratios (95% CIs) of neonatal morbidity after elective cesarean section per week of gestation deliverya
| Outcome | OR (95% CI) | OR (95% CI) | OR (95% CI) | OR (95% CI) | OR (95% CI) | OR (95% CI) |
|---|---|---|---|---|---|---|
| Week of gestation | 37+0–6 | 38+0–6 | 39+0–6 | 40+0–6 | 41+0–6 | ≥42 |
| Primary outcome(including neonatal death)b | 2.4(2.1–2.8) | 1.4(1.2–1.5) | Reference | 0.9(0.8–1.2) | 1.01(0.8–1.3) | 0.9(0.7–1.3) |
| Sepsis | 3.6(1.7–7.7) | 1.7(0.9–3.1) | Reference | 1.8(0.6–5.0) | 1.7(0.5–6.1) | 1.1(0.1–8.3) |
| Combined respiratory outcomec | 3.2(2.5–4.2) | 1.7(1.4–2.1) | Reference | 0.9(0.6–1.3) | 0.8(0.4–1.4) | 0.3(0.1–1.0) |
| Respiratory distress syndrome | 3.8(1.4–10.5) | 1.9(0.8–4.5) | Reference | NA | NA | NA |
| Transient tachypnea of the newborn | 2.9(2.1–3.9) | 1.8(1.4–2.3) | Reference | 1.0(0.6–1.6) | 0.7(0.3–1.4) | NA |
| Intermittent positive pressure ventilation | 6.8(2.3–20.0) | 1.9(0.7–5.3) | Reference | 0.9(0.1–7.6) | 1.5(0.2–12.8) | NA |
| Continuous positive airway pressure | 7.8(4.3–14.5) | 2.3(1.3–4.0) | Reference | 0.3(0.0–2.3) | 0.99(0.2–4.4) | NA |
| Hypoglycemia | 2.1(1.5–2.9) | 1.3(1.1–1.7) | Reference | 1.2(0.8–1.8) | 1.1(0.6–1.9) | 0.98(0.5–2.1) |
| Convulsions | 1.2(0.1–11.9) | 2.0(0.5–7.4) | Reference | 0.8(0.1–7.8) | NA | NA |
| Admission | ||||||
| To the neonatal intensive care unit | 2.8(1.3–5.8) | 1.3(0.7–2.3) | Reference | 0.5(0.1–2.4) | 0.5(0.1–3.5) | NA |
| To any neonatal ward >5 days | 3.1(2.6–3.7) | 1.5(1.3–1.7) | Reference | 0.9(0.7–1.2) | 1.3(0.9–1.7) | 1.2(0.8–1.9) |
| Apgar scored | ||||||
| ≤3 | 3.3(0.2–53.5) | 2.2(0.2–21.6) | Reference | 1.9(0.1–30.6) | NA | NA |
| ≤6 | 3.8(1.6–8.8) | 1.7(0.9–3.5) | Reference | 1.3(0.4–4.6) | 3.6(1.3–10.5) | NA |
| Hyperbilirubinemia | 3.1(1.9–5.1) | 1.1(0.7–1.7) | Reference | 0.4(0.1–1.3) | 1.3(0.5–3.1) | 0.4(0.1–3.0) |
aOdds ratios are adjusted for maternal age |
bPrimary outcome is defined as a composite measure of: neonatal mortality until the 28th day after birth, and/or neonatal morbidity which can consist of any of the following adverse events: severe resuscitation, sepsis, respiratory complications (registered as respiratory distress syndrome |
cCombined respiratory outcome is defined as a composite measure of RDS, TTN, pneumothorax, air leakage, oxygen, IPPV and CPAP; |
d5-minute Apgar score. |
Just like Tita et al,12 we did a subgroup analysis for all births between 38+4-6 weeks (n = 5046). Compared to neonates born at ≥39+0 weeks, neonates born between 38+4-6 weeks still had a significantly higher risk for an adverse neonatal outcome. ORs (95% CI) for primary outcome and for our combined respiratory morbidity were 1.3 (1.1–1.4) and 1.4 (1.1–1.8), respectively. All performed sensitivity analyses showed robustness of our findings (results not shown).
There were no cases of necrotizing enterocolitis or hypoxic-ischemic encephalopathy, and only 3 cases of intracranial bleeding between 38+0-6 weeks.
Comment
We analyzed the neonatal outcome of 20,973 electively performed cesarean sections at term in The Netherlands. More than half of all elective cesarean sections at term were performed <39+0 weeks gestation. As compared with cesarean sections at 39+0-6 weeks, these early planned cesareans had a significantly higher overall risk of various poor neonatal outcome measures, including resuscitation, sepsis, respiratory morbidity and support, admission to the NICU, and prolonged hospitalization. This composite primary outcome occurred in 1 in 5 neonates born between 37+0-6 weeks and in 1 in 8 neonates born between 38+0-6 weeks, which was significantly higher compared to 1 in 10 neonates at 39+0-6 weeks of gestation. The risks of separate adverse neonatal outcomes for delivery at 37 and 38 weeks were also higher. Adjustment for potential confounding variables confirmed the significant trends toward decreasing incidence of neonatal complications with increasing gestational age up to 39 weeks.
The strength of our study is that it comprises recently collected data of almost all deliveries of our country, which results in a large sample size and is therefore a broad reflection of current clinical decision making. Our study has some limitations. First, the reliability of our data depends on the preciseness of registration of obstetricians and pediatricians in the past 7 years. The registration of a planned cesarean section is subdivided into “elective,” “condition mother,” “condition fetus,” and “condition mother and fetus.” After selecting the “elective” cesarean cohort we applied strict exclusion criteria (Figure). However, it is possible that we did not include the complete population of elective cesareans as, for example, obstetricians can register repeat cesarean section under “condition mother” instead of “elective” due to the risk of a uterine rupture during a trial of labor. This might have affected our results, but it is unlikely that those cases would have shown a totally different association between timing of section and outcome than the deliveries investigated in this study. Reliability of the gestational age at birth is also of great importance. The basic care provided in The Netherlands, as is stated in our national guideline regarding prenatal care, is that all women will receive a first-trimester ultrasound to establish/confirm the at-term date. Prenatal care with ultrasound scanning in the first trimester is available for low- and high-risk patients. The PRN database contains a separate question about certainty of the term data. In 97.4% of the births gestational age was registered as certain. If the analysis was restricted to these 97.4%, we observed similar results. The neonatal follow-up in the PRN is not registered for around 32% of all hospitals. We assume that the incidence of neonatal morbidity in these hospitals is not different from those with good neonatal follow-up because both types of hospitals are equally distributed across the country, use the same national clinical guidelines, and are financed similarly. Furthermore, analyses demonstrated that for both hospitals with good and no follow-up, timing of cesarean section rate was similar (results not shown). Socioeconomic status was based on the mean household income level of the neighborhood, which was determined by the first 4 digits of the woman's postal code. Using this proxy measure may have led to some misclassification. However, studies on perinatal mortality in relation to socioeconomic status and neighborhood that were recently carried out in The Netherlands showed neighborhood as a strong indicator for both perinatal outcome and socioeconomic status.21
One could question our decision to exclude all stillbirths. In this large database there have been instances where a woman booked for an elective cesarean section at a particular gestation presented with unexplained stillbirth ≥37+0 weeks. Unfortunately, the exact date of stillbirth is not stated in our database, thus leaving no possibility to perform an intention-to-treat analysis from ≥37 weeks. Moreover, many women with a stillbirth will have had a vaginal delivery after their tragic event, thus making it impossible to distinguish between women who had a stillbirth while waiting for a cesarean section, and women with a planned vaginal delivery who had a stillbirth. However, the effect will be minimal as we are studying low-risk pregnancies. The association between increasing gestational age and diminishing risk of neonatal morbidity until 39+0 weeks of gestation is not new,4, 8, 9, 10, 12 but except for Tita et al,12 these studies had a limited sample size, focused on respiratory morbidity, and analyzed their results in completed weeks of gestation. Compared to previous studies we found lower absolute numbers of respiratory morbidity in all gestational age weeks, although there was a significant increase of respiratory morbidity with decreasing gestational age. Some authors might have used broader definitions for respiratory distress or did not exclude mothers with risk factors for an adverse neonatal outcome.4, 8, 10 To be able to compare our results with these studies we also defined a combined respiratory outcome measure that shows more similar results. Recently, a large prospective study of 13,258 electively performed cesarean sections was published by Tita et al,12 which not only focused on respiratory morbidity but on a composite outcome measure of neonatal mortality and morbidity. To be able to compare our results we defined a similar composite outcome measure of neonatal morbidity. The results of our primary composite outcome are comparable. In contrast with Tita et al,12 our data did not show a significantly higher risk for neonatal morbidity by postponing the cesarean section until ≥40+0 weeks.
Before publication of the analysis of Tita et al12 the significant difference in neonatal morbidity between 38+4-6 weeks and 39+0 weeks was not known. We hope that the results of our study, which are in line with those found by Tita et al,12 will convince more gynecologists to postpone planned cesarean sections until ≥39+0 weeks.
The fear of an increasing number of intrapartum cesarean sections can influence timing and hamper implementation of postponing cesarean sections. Morrison et al8 showed that by altering the planning of elective cesarean sections from 38+0-6 to 39+0-6 weeks only 10% of patients will be in labor before the planned date. Hansen et al4 reported that 25% of intended vaginal deliveries started <39+0 weeks of gestation. In The Netherlands 13.6% of singleton births without congenital malformations started spontaneously between 37+0 and 38+6 weeks' gestation, of which 93.2% ended in a vaginal delivery and 6.8% ended in a secondary cesarean section. It is difficult to compare maternal risks vs benefits of the newborn. Intrapartum cesarean sections may have an increased risk for maternal morbidity and mortality compared with elective cesarean sections.22, 23 Compared to vaginal delivery, cesarean section is associated with an almost 4 times increase in maternal mortality,23 a longer time to recover, and the risk of complication of the operation.24 On the other hand the start of labor or rupture of the membranes could be a benefit for the infants born because of stimulation of surfactant in the fetal lungs.25
We will undertake further studies to analyze factors that can possibly influence neonatal morbidity and therefore must be considered in timing and decision making. Prospective designs will also facilitate exact registration of the number of intrapartum cesarean sections and intrauterine deaths by postponing every planned cesarean section at >39+0 weeks of gestation, and evaluation of the maternal morbidity associated with these intrapartum cesareans, which will enable us to consider maternal risks in timing of elective cesarean sections as well.
Performing elective cesarean sections <39+0 weeks of gestation jeopardizes neonatal outcome and should be avoided whenever possible.
References
- The Netherlands Perinatal Registry (Obstetrics in The Netherlands. Trends 1989-1993). 2005;[Dutch] Bilthoven
- The Netherlands Perinatal Registry (Perinatal care in The Netherlands 2007). 2009;[Dutch] Utrecht
- . Planned cesarean versus planned vaginal delivery at term: comparison of newborn infant outcomes. Am J Obstet Gynecol. 2006;195:1538–1543
- . Risk of respiratory morbidity in term infants delivered by elective cesarean section: cohort study. BMJ. 2008;336:85–87
- . Respiratory distress syndrome in infants delivered by cesarean section. Am J Obstet Gynecol. 1964;88:806–815
- . Mode of delivery and risk of respiratory diseases in newborns. Obstet Gynecol. 2001;97:439–442
- . Neonatal respiratory morbidity risk and mode of delivery at term: influence of timing of elective cesarean delivery. Acta Paediatr. 2004;93:643–647
- . Neonatal respiratory morbidity and mode of delivery at term: influence of timing of elective cesarean section. Br J Obstet Gynaecol. 1995;102:101–106
- . Elective cesarean section is preferred after the completion of a minimum of 38 weeks of pregnancy. [in Dutch] Ned Tijdschr Geneeskd. 1998;142:2300–2303
- . Neonatal respiratory morbidity following elective cesarean section in term infants: a 5-year retrospective study and a review of the literature. Eur J Obstet Gynecol Reprod Biol. 2001;98:9–13
- . Elective cesarean section and respiratory morbidity in the term and near-term neonate. Acta Obstet Gynecol Scand. 2007;86:389–394
- Timing of elective repeat cesarean delivery at term and neonatal outcomes. N Engl J Med. 2009;360:111–120
- The Netherlands Perinatal Registry (Perinatal care in The Netherlands 2006). 2008;[Dutch] Utrecht
- The reliability of perinatal and neonatal mortality rates: differential under-reporting in linked professional registers vs Dutch civil registers. Paediatr Perinat Epidemiol. 2001;15:306–314
- NVOG Richtlijn no. 46: “Basis prenatale zorg” 2002 ((Guideline no. 46: Dutch Society of Obstetrics and Gynaecology: basic prenatal care June 2002)). Utrecht www.nvog.nl2002;Accessed Feb 10, 2010
- . New Dutch reference curves for birthweight by gestational age. Early Hum Dev. 2009;85:737–744
- . Sex differences in fetal lung maturation. Am Rev Respir Dis. 1981;123:205–208
- . Using the outcome for imputation of missing predictor values was preferred. J Clin Epidemiol. 2006;59:1092–1101
- . Regression with missing X's: a review. J Am Stat Assoc. 1992;87:1227–1237
- . A language and environment for statistical computing. R foundation for statistical computing. 2006;Vienna (Austria) http://www.R-project.org/Accessed April 17, 2009
- Perinatal outcomes in the four largest cities and in deprived neighborhoods in The Netherlands. [in Dutch] Ned Tijdschr Geneeskd. 2008;152:2734–2740
- . The relative risks of cesarean section (intrapartum and elective) and vaginal delivery: a detailed analysis to exclude the effects of medical disorders and other acute pre-existing physiological disturbances. Br J Obstet Gynaecol. 1990;97:883–892
- . Pregnancy-related death and health care services. Obstet Gynecol. 2003;102:273–278
- . Intraoperative surgical complication during cesarean section: an observational study of the incidence and risk factors. Acta Obstet Gynecol Scand. 2003;82:251–256
- . Effects of adrenaline and of spontaneous labor on the secretion and absorption of lung liquid in the fetal lamb. J Physiol. 1983;344:137–152
Cite this article as: Wilmink FA, Hukkelhoven CWPM, Lunshof S, et al. Neonatal outcome following elective cesarean section beyond 37 weeks of gestation: a 7-year retrospective analysis of a national registry. Am J Obstet Gynecol 2010;202:250.e1-8.
Reprints not available from the authors.
The racing flag logo above indicates that this article was rushed to press for the benefit of the scientific community.
PII: S0002-9378(10)00082-7
doi:10.1016/j.ajog.2010.01.052
© 2010 Mosby, Inc. All rights reserved.
Refers to article:
-
Latest research from the 2010 meeting of the Society for Maternal-Fetal Medicine
-
Elective delivery before 39 weeks: reason for caution
Volume 202, Issue 3 , Pages 250.e1-250.e8, March 2010
