Genes Impact First-Time Moms: Play Major Role in Pregnancy

How do genes impact fist-time moms? Researchers have analyzed the genomes of thousands of women in the UK and Netherlands in order to measure the extent to which a woman's genes play a role on pregnancy – when she has her first baby and how many children she will have.

In this latest study, the researchers employed recent advances in molecular and quantitative genetics and used existing datasets of 4,300 unrelated women. They then combined these results with data relating to 2,400 women from the UK's largest adult twin registry.

So what did they find? It turns out that genes account for about 15 percent of the differences between modern women when they have their first baby and 10 percent in the differences in the number of children that they have. Overlap between genetic effects also partly explains why women who have children earlier also have a higher number of children.

"In evolutionary and genetic terms, this suggested that younger generations today should be inclined to have children at an earlier age than women in the past," said Melinda Mills, one of the researchers, in a news release. "However, what we actually observe is that the reverse is happening. Social and environmental factors mean women in modern societies are delaying starting families, knowing that there is the risk of becoming infertile if they leave it too late. This research tells us there are genetic differences between women which could be significant for women making decisions about when to have their first baby."

Natural selection isn't just a historical process. Modern societies are still evolving today, with early fertility patterns behind an inherited reproductive advantage.

"In the second half of the 20^th century, women across many societies delayed starting a family," said Felix Tropf, lead author of the new study. "Although genes played a significant part, it seems wider social changes, such as an expansion of women in further education and work, as well as the availability of effective contraception, are having a stronger effect on determining when women in modern societies have children."

The findings are published in the journal PLOS One.

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