More than 50% of neonates born before 34 weeks of gestation in the United States are delivered by cesarean section (CS). When intrauterine growth restriction is present or the neonate is small for gestational age (SGA), vaginal delivery has been reported to be associated with increased odds of neonatal mortality. Given the increased risk of morbidity and mortality for SGA newborns and the relative impossibility of a conclusive randomized controlled trial, this study was performed to examine the association between route of delivery and neonatal outcomes, particularly neonatal death, intraventricular hemorrhage (IVH), and respiratory distress syndrome (RDS), in a large, diverse cohort of preterm SGA newborns.
Data on 1,025,903 singleton live births from 1995 to 2003 were obtained from a data set linking birth certificate and hospital discharge data in New York City. The study population included only women delivering vertex-presenting, singleton neonates between 25 and 34 6/7 weeks of gestation (n = 31,135). Of 23,144 neonates meeting the inclusion criteria, 2885 met the definition for SGA at delivery. Small for gestational age was used as a surrogate for intrauterine growth restriction. Because of the wide range of gestational ages, a subanalysis was done for those with a gestational age less than 30 weeks (n = 359). Another study population included all operative deliveries (n = 2927). Main outcomes included neonatal death before discharge, neonatal RDS, sepsis, IVH, seizure, subdural hemorrhage, or 5-minute Apgar score less than 7. Maternal characteristics included age, parity, race and ethnicity, level of education, insurance status, and prepregnancy weight. Covariates included diabetes, hypertension, and gestational age of delivery.
Of the 2885 neonates, 1214 (42.1%) were delivered vaginally, and 1671 (57.9%) were delivered by CS. All maternal and pregnancy characteristics differed significantly between the 2 groups (P < 0.05). Women who underwent CS were older, heavier, better educated, more likely to be white, and more often had diabetes or hypertension. The rate of CS rose in SGA newborns born at 34 weeks of gestation or less during the course of the study (1995–2003; 50% and 61% in 1995 and 2003). Neonates delivered by CS had a higher incidence of RDS and 5-minute Apgar scores of less than 7 compared with those delivered vaginally (odds ratio [OR], 1.49; 95% confidence interval [CI], 1.25–1.76; and OR 1.42; 95% CI, 1.07–1.87, respectively). After adjustment for maternal age, race, parity, education, insurance status, prepregnancy weight, diabetes, hypertension, and gestational age at delivery, CS was still associated with increased odds of RDS compared with vaginal delivery (adjusted OR, 1.32; 95% CI, 1.07–1.63) and tended to be associated with slightly elevated risks for all outcomes except IVH and neonatal death. When forceps and vacuum deliveries were included in the analysis, results were not altered significantly.
The fact that CS is associated with more RDS indicates that CS is not necessarily beneficial to SGA preterm neonates. The known risks and costs of CS might be justified if CS improves neonatal outcomes. However, these results show that CS compared with vaginal delivery was not associated with any statistically significant benefit for preterm SGA neonates. Further research is necessary to evaluate the effects of the rising CS rate in preterm SGA neonates. As with full-term newborns, vaginal delivery offers neonates an early respiratory advantage compared with CS.