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Pregnant pause: women who delay motherhood after 30 risk bequeathing infertility to their daughters.

A new study suggests older mothers may bequeath a devastating legacy by passing on biological flaws that will make it more difficult for their own daughters to get pregnant.

Dramatic findings from a US study of almost 80 women undergoing fertility treatment shows those who failed to conceive had older mothers than those who succeeded.

These mothers had a shorter ‘window of fertility’ between giving birth to their daughters and hitting the menopause.

For the first time, researchers have calculated the ‘age’ of eggs at the time of conception and linked it with the fertility potential of the daughters that were born subsequently.

The findings indicate that older eggs may carry inbuilt defects that only become apparent when female children attempt to get pregnant.

Dr Peter Nagy, a leading fertility specialist at Reproductive Biology Associates, a fertility clinic in Atlanta, said postponing childbirth had implications for women that could cascade down the generations.

“For every year that a woman delays childbirth, it becomes more difficult for her daughters. Women will be asking whether their decision not only affects their own chances of getting pregnant but the chances for their daughters.”

“Today we see a lot of women delaying motherhood and there could be consequences in 20 or 30 years’ time, we could see more fertility problems in the future.”

He said it was well known that older women had trouble getting pregnant because they had “aged eggs” but it had never been shown before that this might lead to subtle defects in the fertility potential of girls born as a result, making it harder for them to conceive.

Dr Nagy acknowledged the study dealt only with women already struggling with fertility problems.

But he said: “We need data on the general population to confirm this, but we think we’re going to get it.”

Dr Nagy presented his data at the American Society for Reproductive Medicine annual meeting in New Orleans.

The latest study comes amid growing concern among doctors in Britain over the ‘epidemic of pregnancy’ in women in their 30s, when the risks of childbirth to mother and baby increase, and rising infertility rates.

Around half of births today are to mothers aged 30-plus. Twenty years ago the proportion was just 27 per cent.

The average age of all new mothers, married and single, is 29.4, the highest level since the Second World War.

Last year some of the country’s leading obstetricians and fertility specialists warned that women who put off having children until their 30s were ‘defying nature’ and risk never becoming mothers.

Writing in the British Medical Journal, consultant obstetrician Dr Susan Bewley warned that fertility problems increase with age.

“Women want to ‘have it all’, but biology is unchanged” she said. “If women want room to maneuver, they are unwise to wait until their 30s.”

Lord Robert Winston has also warned that women are sacrificing maternal happiness for career success. He said it was a “social problem” that could be remedied by measures encouraging young women to take time out from their careers.

In the new study, Dr Nagy and colleagues set out to discover whether increasing maternal age might affect the ability of daughters born to have children of their own.

Almost 80 women seeking fertility treatment, who were all under 35 years, were asked three questions. They had to give the age of their mothers and fathers when they were born, and the age at which their mother went through the menopause.

The patients’ husbands were asked similar questions.

The information was analyzed according to whether the patients – who all had standardised treatment – had managed to become pregnant.

The average maternal age of mothers of women in the group which succeeded in getting pregnant was 25 years, compared with 28 years in women who did not get pregnant.

The average age of fathers of women who got pregnant was 28 years, compared with nearly 32 years in the group which was not pregnant.

The average time span between the age at which the mothers gave birth to their daughters and their menopause was almost 25 years for women who got pregnant using fertility treatment.

But it fell to less than 20 years among women who did not get pregnant – showing their mothers had a much shorter ‘window’ of fertility before their menopause.

As a result the eggs that led eventually to their daughters being born would have been five years older on average.

Although the age of the mothers when they got pregnant does not appear particularly advanced, the statistical analysis of the figures produces a significant difference between the two groups of women having fertility treatment.

Dr. Nagy said the key to a woman’s reproductive ability was the age of her eggs – she is born with a finite supply and they become increasingly less able to be fertilized as she gets older.

He said “A 25-year-old woman has a 90 per cent chance of a healthy pregnancy and baby whereas a 40-year-old woman’s chances in the same circumstances fall to 10 per cent, simply because her ovaries and eggs are ageing.”

He said the possible reason for fertility problems being handed down to daughters was subtle defects in ‘aged’ eggs that affects embryonic cell development but remains latent until they get pregnant themselves.

Then the development of their own eggs works less effectively, making them more likely to be infertile, he said.

[24Oct06,, J. Hope]