Azara Blog: Obesity and Caesareans are both correlated with stillbirths

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Date published: 2008/06/07

The BBC says:

Having a Caesarean does not raise the risk of a stillbirth in a subsequent pregnancy, a study has found.

The University of Calgary study contradicts previous research which suggested an increased risk.

The study suggests a mother's obesity - not whether she has a Caesarean - may instead be the key factor.

The study, which appears in the journal BJOG, suggests that previous research has failed to take this factor properly into account.

However, health professionals advise woman not to opt for a Caesarean lightly, as it is a major surgical procedure, with a risk of complications.

Researcher Dr Stephen Wood said the finding was particularly important as the number of Caesareans had increased in recent years.

He said obesity had been consistently linked to both Caesareans and stillbirths, but it had proved difficult to tease out its independent effect on each.

The Calgary study examined 157,029 second births, and took potentially confounding factors, such as maternal weight, into consideration.

Once they had done that they found that, among women who had previously had a Caesarean, the stillbirth rate was 2.1 per 1,000, compared with 1.6 per 1,000 in women who had no Caesarean history - not a statistically significant difference.

The researchers admit that they were not able to completely account for maternal weight, but had done so far more than previous research.

In short, there is a correlation between stillbirths and Caesareans and obesity, and as usual correlation is not the same thing as causation. So it is not clear if Caesareans or obesity is "causing" the stillbirths or even if there is yet another factor not yet discovered that is the "cause" or whether the whole situation is just too complex to ever have hope of finding the "cause". Unfortunately, in the world of health, just finding a correlation (which is a relatively trivial thing to do) is enough to get acres of media coverage, with an implied causation happily stated. So this story is happy to run with obesity as the "key factor" in stillbirths and previous stories have evidently been happy to run with "Caesareans" as the "key factor". These kinds of stories usually tell us more about the prejudices of the researchers (and the media) than anything else. The only way to do the research here properly would be to randomly choose which women receive Caesareans and which do not, and needless to say, this research will never be done.

At least this article points out that in fact this correlation between Caesareans and stillbirths should not be the most important factor when considering a Caesarean. That's another thing about these health stories and correlations implied to be causations. They usually miss the bigger picture.

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