Elsevier

The Lancet

Volume 362, Issue 9398, 29 November 2003, Pages 1779-1784
The Lancet

Articles
Caesarean section and risk of unexplained stillbirth in subsequent pregnancy

https://doi.org/10.1016/S0140-6736(03)14896-9Get rights and content

Summary

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 120 633 singleton second births, there were 68 antepartum stillbirths in 17 754 women previously delivered by caesarean section (2–39 per 10 000 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% Cl 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.

Introduction

Rates of caesarean section have risen substantially in recent years.1 The causal factors are complex and incompletely understood.2, 3 Concerns have been expressed about potential adverse effects, especially in relation to short-term morbidity in the mother and child.4, 5 Studies on the effects of previous caesarean section on future pregnancies have focused mainly on the maternal and fetal risks of scar rupture associated with vaginal birth.6, 7 However, it has also been noted that placental complications, such as abruption and placenta praevia, are more common in women who have previously undergone caesarean section,8, 9 and the association with abruption has been observed in women with no previous history of abruption and is independent of obvious confounders.10 The effect of previous caesarean delivery on the risk of antepartum perinatal death in subsequent pregnancies is not known. We did a large-scale, retrospective, cohort study to establish whether caesarean delivery in a first pregnancy was associated with an increased risk of antepartum stillbirth in the second.

Section snippets

Data sources

The Scottish Morbidity Record (SMR2) collects information on clinical and demographic characteristics and outcomes for all patients discharged from Scottish maternity hospitals. The register is subjected to regular quality assurance checks and has been more than 99% complete since the late 1970s.11 A quality assurance exercise was done in 1996–97 in which 5% of case records (n=1414) were compared with the SMR2 database during a 6-month period. All fields used in the present study had fewer than

Results

There were 411 685 singleton births in Scotland between 1992 and 1998, excluding deaths due to fetal abnormality or rhesus isoimmunisation; 144 202 (35%) were second births. Of these, 408 (0·3%) did not have information for gestational age or birthweight, or these values were outside 24–43 weeks or less than 500 g, respectively. Of the remaining 143 794 records, data were missing for previous caesarean delivery in 14 (<0·1%), height in 12866 (9·0%), deprivation category in 448 (0·3%), smoking

Discussion

Our results show that women whose first birth was by caesarean section were at significantly increased risk of having an antepartum stillbirth in their second pregnancy, mainly because of increased risk of unexplained stillbirth. The association with unexplained stillbirth was not attenuated by adjustment for maternal age, height, smoking status, social deprivation, and interpregnancy interval, or for key outcomes of the first pregnancy: birthweight percentile, preterm delivery, and perinatal

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