The older your mother was when you were born, the less likely you are to have children – but we don’t know why. An analysis of thousands of women has found that daughters of older mums are more likely to be childless – an effect that can’t be fully explained by social factors like wealth or education.
So far, there’s been mixed evidence over whether parental age at first birth is linked to lower fertility in children. There does seem to be a trend that women who are wealthier and more educated are more likely to give birth later in life – and wealth tends to be passed down the generations for multiple reasons.
ܳ, of McGill University in Montreal, Canada, is interested in whether there might also be biological factors that make the children of older parents less likely to have children of their own.
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Her team analysed data from over 43,000 women in the US who were born between 1930 and 1964. More than 19 per cent of women born to mothers aged 30 or over went on to be childless. That compares with about 15 per cent in women whose mothers had been aged 20 to 24 at the time of their birth and less than 13 per cent of those born to teenage mothers.
Women who had a post-graduate degree were the most likely never to have any children, followed by women who had never married, and women who were lesbian.
Analysis of the figures revealed, however, that having higher levels of education or never marrying could not fully account for the levels of childlessness in women born to older mums. Even among women who held a postgraduate degree, those born to older mothers were more likely to be childless.
Unknown cause
Could the effect be caused by older mums passing on fertility problems? The results suggest not, as women with older mothers were just as likely to report difficulty conceiving as women with younger mothers. This leaves the reasons for higher childlessness among the daughters of older mothers unclear.
“It is possible that being born to an older mother results in daughters behaving differently,” Basso suggests. If true, this may have some biological cause, or it may be caused by some other factor.
“These results surprise me, and they are important to pursue,” says , of the National Institute of Environmental Health Sciences, North Carolina, who says that childlessness seems to be increasing in Europe and perhaps elsewhere. “Childlessness is becoming a political and social concern. If some of this increase is due to older mothers in the previous generation – whatever the causal mechanism – it would be good to know.”
Human Reproduction
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