NEW YORK -- June 16, 2008 -- A new study published in BJOG: An International Journal of Obstetrics and Gynaecology has found that, contrary to the findings in other recent research, a previous caesarean section does not increase the risk of stillbirth in the second pregnancy.
Researchers from the University of Calgary, Calgary, Alberta, investigated the connection because they were concerned that previous research had failed to account for the effect of maternal obesity, which is associated with both caesarean birth and stillbirth.
The study included 157,929 second births with information obtained on demographic characteristics, pregnancy complications, mode of delivery, and outcome of live or stillbirth. Information on factors that could impact on the results such as maternal diabetes, maternal weight, hypertension, and smoking during pregnancy was also extracted. However, exact maternal weight data was not available; therefore, women were categorised as either less than or greater than 91 kg.
Initially the study looked at the total number of antepartum stillbirths in both groups. Overall, there were 331 antepartum stillbirths giving a rate of 3.0/1,000 in the previous caesarean group compared with 2.7/1,000 in the previous vaginal-delivery group.
The data were then adjusted to exclude other potential contributing factors such as significant fetal abnormality, maternal trauma such as a motor vehicle accident during pregnancy, and infection such as cytomegalovirus. Once these factors were taken into account, there were a total of 265 antenatal stillbirths -- 63 (2.1/1,000) in the previous caesarean group and 202 (1.6/1,000) in the previous vaginal-birth group.
Further, the data prior to 1996 did not include complete information on a number of significant factors such as maternal weight, smoking during pregnancy, pre-pregnancy diabetes, and hypertension. The data were again adjusted to exclude these participants from the final analysis, thus, the sample size reduced from 157,929 to 132,590 and the stillbirth number reduced from 265 to 210. In this analysis, previous caesarean section did not demonstrate a statistically significant increase in stillbirth risk.
"Our study strongly suggests that previous caesarean section does not increase the risk of stillbirth in subsequent pregnancies. Although previous research has made a link between the two, it is likely that maternal obesity played a part as it was not controlled for," said study author Stephen Wood, MD, Department of Obstetrics and Gynaecology, University of Calgary, Calgary, Alberta.
"Obesity has been a consistently observed risk factor for both stillbirth and caesarean section. It has been difficult for investigators, including us, to adequately control for this factor as good anthropometric data is often not available in large perinatal databases. Indeed we were limited to using maternal weight of 91 kg or more as a cut-off for obesity; however, this is more than other studies have done. As caesarean section is increasingly common, and stillbirth is a very important outcome, further research in this area is required."
SOURCE: Royal College of Obstetricians and Gynaecologists
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