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.
In The Netherlands the incidence of a cesarean section has increased from 8.5% in 1993 to 15.1% in 2007. 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. 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 . 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 al 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. 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.
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, 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.
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, ethnicity, parity, socioeconomic status, fetal gender, and fetal position. 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, using R software (The R Foundation, Vienna, Austria). 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.
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 ).
| 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 delivery a | ||||||
| Mean, y b | 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 group a | ||||||
| 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) |
| Parity a | ||||||
| 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 status a | ||||||
| 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 | ||||||
| Sex a | ||||||
| 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) |
| Position a | ||||||
| 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) |
| Birthweight a | ||||||
| Mean – g c | 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) |
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