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This is an interesting study but it by no means establishes that men born to overweight women are more likely to be infertile.
Sadly that hasn’t stopped @MetroUKnews printing a horrible headline about “fat mothers” putting their children at risk.
Sadly that hasn’t stopped @MetroUKnews printing a horrible headline about “fat mothers” putting their children at risk.
The study followed a large Danish cohort of women who were pregnant in 1984-7 and their children into adulthood. Information on their children’s fertility was obtained by checking Danish health registers for fertility problems or IVF treatment.
Cue our first query. The sons and daughters in the study are now only between 31-34 years old. Given the average age of parenthood in Denmark is currently 31 for mothers & 33.5 for fathers, it’s very likely the information on these registers is incomplete.
This approach conceptualises infertility is a binary outcome, which of course we know is not the case.
It also assumes everyone with infertility had sought medical help, which doesn't necessarily happen in practice. And conversely it assumes everyone who sought help was definitely infertile (although the authors did try to correct for this)
Next note of caution: turns out the Danes were pretty slim in the 80s, so there were very few overweight women in the study to begin with. Of a total of 9232 children, only 1203 were born to women with a BMI of 25 or more, compared to 7143 born to women in normal weight range.
For this reason, the study could not separate overweight and obese mothers, so they were all combined into one group of women with BMIs over 25. (When BMI was treated as a continuous variable, the results for BMIs over 30 were inconclusive.)
Next there’s a problem with the way the figures have been reported in the media. We’ve got to start including absolute risk as standard!
@MetroUKnews reports “boys born to overweight women are 40 per cent more likely to be infertile”, which sounds huge, but actually it was an increase from 7% to 10%.
The confidence interval was also relatively wide, ranging from 1.0 (no association) to 1.9 (risk almost double).
The confidence interval was also relatively wide, ranging from 1.0 (no association) to 1.9 (risk almost double).
There are many possible factors that could have caused this association, only some of which are acknowledged and adjusted for by the authors. None of the children’s lifestyle factors are included for example.
Basically a lot more research is needed before we'll know if there's a causal link between higher maternal weight & sons’ infertility. Meanwhile, at a time when pregnant women are already incredibly anxious, was it really necessary to print such a scary headline @MetroUKnews?
