Tuesday, April 29, 2008

New study shows no increase in stillbirth after C-section

A new paper in the May issue of the British Journal of Obstetrics and Gynecology was unable to replicate an important paper that claimed that C-section increases the risk of unexplained stillbirth in a subsequent pregnancy. The issue is explained by the editor of BJOG in an accompanying editorial:
For many years, there have been calls to reduce the caesarean section rate in developed countries, and yet year on year, the rate continues to increase—while the maternal mortality continues to fall. Those who argue for a reduction have to persuade women ... to pursue more doggedly a vaginal birth. Reports of the adverse effects of caesarean section are grist to their mill, and certainly, the increased rate of percent of praevia and accreta in subsequent pregnancies (together with the increased risk of caesarean hysterectomy) appears indisputable. A paper ... in the Lancet in 2003, which reported that the risk of 'unexplained' stillbirth after 39 weeks of gestation was more than doubled following a previous caesarean section ... attracted a lot of attention and has to date been cited 64 times (which is a lot!)... Wood et al. report a study of more than 158,000 second births in Alberta Canada and found no significant difference in the rate of unexplained antepartum stillbirth by mode of first delivery after adjusting for maternal age and blood pressure. Will their findings be equally highly cited?
The paper, The risk of unexplained antepartum stillbirth in second pregnancies following caesarean section in the first pregnancy seems to be a comprehensive study of 158,502 second births. The analysis showed:
The stillbirth rate in the group with a previous caesarean section was 4.6/1000 compared with 3.9/1000 in the previous vaginal delivery group (P = 0.10). Of the stillbirths, 21% in the previous caesarean section group and 19% in the previous vaginal delivery group were intrapartum. The antepartum stillbirth rate was 3.0/1000 in the previous caesarean section group compared with 2.7/1000 in the previous vaginal delivery group (P = 0.46)...

Our study did not demonstrate an increased risk of unexplained antepartum stillbirth in second pregnancies in women who had had a previous caesarean section. This result is in contrast to a previous similar study of Scottish women... [F]ive other studies have evaluated stillbirth risk in pregnancies following caesarean section with mixed results...

It is apparent that an increased risk of stillbirth in pregnancies after caesarean section has not been consistently observed... [D]ifferences in stillbirth definitions or uncontrolled confounding factors are the most likely explanations. The initial Scottish study that generated interest in this question restricted analysis to antepartum stillbirths, and their primary finding was an increased risk of unexplained stillbirth.
The authors address the question of why their results differ from the Scottish study:
... Our study was unable to replicate the findings of the previous Scottish study, which reported a significant increased risk of unexplained stillbirth in women who had had a previous caesarean section. One possible explanation for this variability in results is the slightly differing definitions of unexplained stillbirths between the two studies. Although this is possible, we do not believe that differences in the definition of unexplained stillbirth would have affected our results... [W]e feel that it would be highly unlikely that a change in the definition of 'unexplained' stillbirth would differentially increase the proportion of stillbirths in the previous caesarean section group to the point that a statistically significant association emerged...

... As the association between previous caesarean section and total stillbirth or unexplained stillbirth has not been consistently observed, we think it would be very premature to conclude a causal association exists. However, given the important potential public health implications, further research on this question should be undertaken with other large perinatal databases.


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