In vitro is chauvinist: The sex ratio of IVF babies is skewed towards males

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In vitro fertilization (IVF) accounts for up to five percent of babies born in developed countries, and the technique has yielded some five million people ever since Louise Brown was born in the UK on July 25, 1978. And that’s just humans; the technology has been a huge boon in breeding farm animals. Yet there are hints that the procedure can have some unwanted effects on the resultant embryos. One such indication is a skewed sex ratio.

The sex ratio of a population should be roughly fifty-fifty. That ratio is sensitive, and possibly adaptive, to a number of environmental factors like maternal nutrition and population density. It's thus viewed as an indicator of reproductive health.

But in 1991, it was noted that IVF generates more bulls than heifers; the same skewing towards males has since been seen in pigs, mice—and, yes, people. A new paper in PNAS offers an explanation of what is going on and how to fix it.

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