Of 1,399 infants born to women with an estimated date of delivery on or before February 29, 2008, 1,194 met inclusion criteria for these analyses. depicts the derivation of the study population.
Derivation of the study population (n=1,194). Starting number is the total number of infants.
Overall, 566 (47%) women were delivered vaginally, 216 (18%) by nonelective cesarean, and 412 (35%) by elective cesarean delivery. Participants recruited intrapartum or postpartum had higher rates of cesarean delivery (). depicts the mode of delivery by birth year. Overall, cesarean delivery rates ranged from 49% to 54%. There was no significant association of mode of delivery by year of delivery (P=.71). The most common primary indications for elective cesarean were interruption of HIV-1 transmission (39.3%), repeat (29.8%), participant request (5.8%), nonreassuring fetal heart rate (4.8%), and hypertension or preeclampsia (4.6%). For nonelective cesarean delivery, the most common primary indications were nonreassuring fetal heart rate (21.8%), interruption of HIV-1 transmission (21.3%), repeat (17.1%), and labor arrest disorder (9.3%). There were significant differences in the median infant gestational age (weeks) at delivery according to mode of delivery: vaginal (median=38.8; 25th and 75th percentile=37.6, 39.7), nonelective cesarean delivery (median=38.0; 25th and 75th percentile=36.4, 39.4), and elective cesarean delivery (median 38.1; 25th and 75th percentile=37.7, 38.4) (P<.001).
Characteristics of the Study Population Overall and According to Mode of Delivery
Rates of mode of delivery by birth year (n=1,194). As a result of the partial year data, 2002 and 2008 births were regrouped into 2003 and 2009 births, respectively.
Characteristics of the study population, overall and according to mode of delivery, are shown in . Several maternal characteristics were associated (P≤.10) with mode of delivery: race and ethnicity, parity, timing of study enrollment, maternal diabetes, and CD4 count and plasma viral load closest to delivery. Infant characteristics by mode of delivery also are shown in . The overall rate of preterm birth was 16.9% and of low birth weight was 13.0%. Preterm infants and low-birth-weight infants were more likely to be delivered by nonelective cesarean. The overall rate of mother-to-child transmission of HIV-1 was 0.4%.
Overall, 43 (3.6%) of infants had respiratory distress syndrome, 36 (3.0%) had transient tachypnea of the newborn, 12 (1.0%) had meconium aspiration, four (0.3%) had pneumonia, and one (0.1%) had pneumothorax. As a result of small numbers of cases of meconium aspiration, pneumonia, and pneumothorax, no further analyses of these outcomes were conducted. Associations between mode of delivery with respiratory distress syndrome and with transient tachypnea of the newborn are shown in . Mode of delivery was associated with respiratory distress syndrome (P=.001) but was not associated with transient tachypnea of the newborn (P=.37).
Association Between Mode of Delivery and Infant Respiratory Distress Syndrome and Transient Tachypnea of the Newborn
The distribution of gestational ages according to mode of delivery for those 43 infants with respiratory distress syndrome is shown in . The majority of infants with respiratory distress syndrome had gestational ages at birth of 34 weeks or greater. Over 30% had gestational ages at birth of more than 37 weeks. The proportions of infants with respiratory distress syndrome were: 37 weeks (7 of 219 [3.4%]), 38 weeks (4 of 388 [1.0%]), and 39 weeks (3 of 208 [1.1%]). There were no cases of respiratory distress syndrome at 40 weeks or beyond in 177 infants. Fisher’s exact comparison of mode of delivery and respiratory distress syndrome among term infants showed no significant difference (but may be prone to type 2 error as a result of low numbers of cases).
Gestational age at delivery for neonates with respiratory distress syndrome (RDS) (n=43).
In evaluation of the infants with respiratory distress syndrome, timing of study enrollment, maternal viral load, infant gestational age at delivery, and infant low birth weight were associated with respiratory distress syndrome in univariable analyses and were considered as potential confounders in multivariable analyses. Although gestational age and low birth weight are related to one another, multivariable analysis results were similar when either variable was dropped. The final multivariable logistic regression model assessed the association between mode of delivery and infant respiratory distress syndrome adjusting for maternal race and ethnicity and infant sex (identified a priori), maternal plasma viral load closest to delivery, infant gestational age, and infant birth weight. In the final model, there was no statistically significant association between mode of delivery and infant respiratory distress syndrome (P=.10) (). However, there was a trend toward an increased risk of respiratory distress syndrome among infants delivered by cesarean compared with vaginal delivery (elective cesarean delivery compared with vaginal delivery: OR 2.32, 95% CI 0.95–5.67; nonelective cesarean delivery compared with vaginal delivery: OR 2.56, 95% CI 1.01– 6.48). Infant preterm birth (P=.002) and low birth weight (P<.001) were significantly associated with infant respiratory distress syndrome.
Unadjusted and Adjusted Odds Ratios for Mode of Delivery and Respiratory Distress Syndrome