First birth cesarean and risk of antepartum fetal death in a subsequent pregnancy.

Introduction: To examine the relationship between first birth by cesarean and antepartum fetal death in a subsequent pregnancy in a large, hospital-based population.

Methods: Data for this retrospective cohort study were taken from a database of all women who gave birth at Brigham and Women's Hospital during 4 waves of data collection beginning in 1994 and ending in 2002. We calculated the risk of antepartum fetal death in the subsequent pregnancy for women whose first birth was by cesarean compared to women with a vaginal first birth. Survival analysis was used to examine the influence of gestational age at birth.

Results: Of 10,996 women who met inclusion criteria, 22% (n = 2450) had first births by cesarean, and 78% (n = 8546) had vaginal first births. The risk of antepartum fetal death in the subsequent pregnancy for women whose first birth was by cesarean was significantly greater than the risk for women whose first birth was vaginal (odds ratio 2.6; 95% confidence interval, 1.1-6.2). The relationship between first birth cesarean and antepartum fetal death in a subsequent pregnancy differed by gestational age at birth, with no excess risk among women with a previous cesarean birth who gave birth before 34 weeks' gestation but with a substantially increased risk for women who gave birth at 34 or more weeks' gestation (unadjusted hazard ratio = 5.6; 95% confidence interval, 1.6-19.8). Hazard ratio estimates for the association remained significant in bivariate models when adjusted for maternal height, weight, age, hypertension, and diabetes.

Discussion: In these data, first birth by cesarean was associated with an increased risk of antepartum fetal death in a subsequent pregnancy. Our findings suggest that antepartum fetal deaths in subsequent pregnancies might be prevented by avoiding primary cesarean birth.