Very young and middle-aged mothers produce offspring with lower bodyweights and smaller reproductive organs than the offspring of 鈥榶oung adult鈥� mothers, a study of mice has found.
What鈥檚 more, the weight effect was passed on to the 鈥榞randchildren鈥� of the original mouse mothers. These descendants had lower than average birthweights.
The scientists Ming-Hseng Wang and Frederick vom Saal of the University of Missouri call for further research, as 鈥渧ery early and very late pregnancies are becoming common in humans鈥�.
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鈥淭here haven鈥檛 been any long-term studies looking at the outcomes of babies born to very young or much older mothers,鈥� says Richard Kennedy of the Centre for Reproductive Medicine at Walsgrave Hospital, Coventry, England. 鈥淭hese are interesting findings.鈥�
The pups born to very young and middle-aged mothers also began puberty later. Low birthweight and later bodyweight, as well as age at puberty, have been linked to reduced fertility. Fertility could also be affected by a reduction in the size of the reproductive organs.
Kennedy thinks searching for links between maternal age and fertility could be fruitful. 鈥淚t wouldn鈥檛 be hard to include the mother鈥檚 age of conception for men with low sperm counts,鈥� he says.
Wang and vom Saal think the effects may be caused by age-related changes in the mothers鈥� hormone patterns. Very young and middle-aged pregnant mice had lower levels of oestrogen and different patterns of testosterone compared with the pregnant young adult mice, they found.
The mother鈥檚 age had different effects on male and female pups. Female mice born to very young or very old mothers completed puberty significantly later than other pups. Female offspring of very young mothers had the lowest bodyweights of all the pups.
Maternal age affected the size of the reproductive organs in male pups, but not females. Male offspring of the young adult mothers had higher bodyweights and heavier testes than the other male pups.
Maternal oestrogen and testosterone 鈥榠mprint鈥� the function of cells in the reproductive organs, brain and many other tissues of a foetus, say Wang and vom Saal.
All the pups in the experiment were fostered by young adult mice to ensure that behavioural differences related to the mother鈥檚 age were not affecting the pups鈥� development.
Source: Nature (vol 407, p 469)