Term Cesarean Delivery in the First Pregnancy is Not Associated with an Increased Risk for Preterm Delivery in the Subsequent Pregnancy.

BACKGROUND: Prior studies have reported an increased risk for preterm delivery following a term cesarean delivery. However, these studies did not adjust for high risk conditions related to the first cesarean delivery and are known to recur.

OBJECTIVE: To determine if there is an association between term cesarean delivery in the first pregnancy and subsequent spontaneous or indicated preterm delivery.

STUDY DESIGN: This was a retrospective cohort study of women with the first two consecutive singleton deliveries (2007-2014) identified through a linked pregnancy database at a single institution. Women with a first pregnancy that resulted in cesarean delivery at term were compared to women whose first pregnancy resulted in vaginal delivery at term. Exclusion criteria were known to recur medical or obstetrical complications during the first pregnancy. A propensity score analysis was performed by matching women that underwent a cesarean delivery with those that underwent a vaginal delivery in the first pregnancy. The association between cesarean delivery in the first pregnancy and preterm delivery in the second pregnancy in this matched set was examined using conditional logistic regression. The primary outcome was overall preterm delivery <37 weeks in the second pregnancy. Secondary outcomes included type of preterm delivery (spontaneous versus indicated), late preterm delivery (34-36 6/7 weeks), early preterm delivery (< 34 weeks), and small for gestational age (SGA) birth.

RESULTS: Of a total of 6,456 linked pregnancies, 2,284 deliveries were matched; 1142 were preceded by cesarean delivery and 1142 were preceded by vaginal delivery. The main indications for cesarean delivery in the first pregnancy were dystocia in 703 (61.5%), non-reassuring fetal status in 222 (19.4%), breech presentation in 100 (8.8%), and other in 84 (7.4%). The mean (standard deviation) gestational ages at delivery for the second pregnancy was 38.8 (1.8) and 38.9 (1.7) weeks, respectively, for prior cesarean delivery, and vaginal delivery. The risks of preterm delivery in the second pregnancy among women with a previous cesarean and vaginal delivery were 6.0% and 5.2%, respectively (adjusted odds ratio [aOR] 1.46, 95% confidence interval [CI] 0.77 - 2.76). In an analysis stratified by the type of preterm delivery in the second pregnancy, no associations were seen between cesarean delivery in the first pregnancy and spontaneous preterm delivery (4.6% versus 3.9%; aOR 1.40, 95% CI 0.59 - 3.32) or indicated preterm delivery (1.6% versus 1.4%; aOR 1.21, 95% CI 0.60 - 2.46). Similarly, no significant differences were found in late preterm delivery (4.6% versus 4.1%; aOR 1.13, 95% CI 0.55 - 2.29), early preterm delivery (1.6% versus 1.2%; aOR 1.25, 95% CI 0.59-2.67), or neonates with birthweight <5th percentile for gestational age (3.6% versus 2.2%; aOR 1.26, 95% CI 0.52 - 3.06).

CONCLUSION: After robust adjustment for confounders through a propensity score analysis related to the indication for the first cesarean delivery at term, cesarean delivery is not associated with an increase in preterm delivery, spontaneous or indicated, in the subsequent pregnancy.