A study of women born in the Netherlands in the 19th century adds to the evidence that the daughters of older mothers may be less fertile.
Many animal studies have found that females born to older mothers have worse health and fewer offspring on average. This could be because eggs accumulate mutations as they age.
Some studies suggest the same is true of people, but in modern populations factors such as education, wealth and access to contraception have a big effect on the average number of children women have, making it hard to identify whether a mother鈥檚 age does affect her daughter鈥檚 fertility.
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To try to get around this, Ingrid van Dijk at Lund University in Sweden and her colleagues used data on births, deaths and marriages in the Dutch province of Zeeland during the 19th century. They looked at more than 7000 mothers, who collectively gave birth to nearly 10,000 daughters between 1812 and 1874, and who also had a collective total of just over 73,000 grandchildren born before 1914.
They found that with every year鈥檚 increase in the mother鈥檚 age, there was a 0.3 per cent decrease in the number of children each daughter had. The effect is small, but statistically robust, the team says.
鈥淚 think that there are some advantages to using historical populations for this type of study,鈥� says Olga Basso at McGill University in Canada. 鈥淲omen were expected to marry and have children, and most did.鈥�
This suggests childlessness was rarely voluntary, she says. By contrast, today many women choose not to have children.
However, it isn鈥檛 clear that the lower number of children in daughters with older mothers in Zeeland is due solely to a biologic effect of maternal age, says Basso. For instance, the team excluded mothers who died before the age of 50, which might have biased the results.
Zsolt Nagy at Reproductive Biology Associates in Atlanta, Georgia, thinks the findings are valuable but agrees with Basso. 鈥淎lthough this approach may eliminate some of the confounding factors, many other confounding factors may remain,鈥� he says.
The team didn鈥檛 look at the effects of paternal age, but other studies suggest that the children of older fathers also have reduced fertility. Older fathers pass on more mutations than older mothers.
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