Caesarean section and risk of unexplained stillbirth in subsequent pregnancy.

BACKGROUND

Caesarean section is associated with an increased risk of disorders of placentation in subsequent pregnancies, but effects on the rate of antepartum stillbirth are unknown. We aimed to establish whether previous caesarean delivery is associated with an increased risk of antepartum stillbirth.

METHODS

We linked pregnancy discharge data from the Scottish Morbidity Record (1980-98) and the Scottish Stillbirth and Infant Death Enquiry (1985-98). We estimated the relative risk of antepartum stillbirth in second pregnancies using time-to-event analyses.

FINDINGS

For 120633 singleton second births, there were 68 antepartum stillbirths in 17754 women previously delivered by caesarean section (2.39 per 10000 women per week) and 244 in 102879 women previously delivered vaginally (1.44; p<0.001). Risk of unexplained stillbirth associated with previous caesarean delivery differed significantly with gestational age (p=0.04); the excess risk was apparent from 34 weeks (hazard ratio 2.23 [95% CI 1.48-3.36]). Risk was not attenuated by adjustment for maternal characteristics or outcome of the first pregnancy (2.74 [1.74-4.30]). The absolute risk of unexplained stillbirth at or after 39 weeks' gestation was 1.1 per 1000 women who had had a previous caesarean section and 0.5 per 1000 in those who had not. The difference was due mostly to an excess of unexplained stillbirths among women previously delivered by caesarean section.

INTERPRETATION

Delivery by caesarean section in the first pregnancy could increase the risk of unexplained stillbirth in the second. In women with one previous caesarean delivery, the risk of unexplained antepartum stillbirth at or after 39 weeks' gestation is about double the risk of stillbirth or neonatal death from intrapartum uterine rupture.