ArticlesCaesarean section and risk of unexplained stillbirth in subsequent pregnancy
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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