WOMEN in their late thirties and forties who give birth to girls may compromise their daughters’ own chances of starting a family.

Advancing age not only reduces a woman’s ability to conceive but also raises the risk that her female offspring will struggle to conceive later in life, scientists claim.

Their findings are alarming because women are increasingly postponing having children until they have established a career. One in seven couples already has difficulty becoming pregnant, and this is likely to worsen as more daughters of older mothers reach adulthood.

In Britain, half of all births are to mothers over 30, compared with 27 per cent 20 years ago. Over-35s account for 9 per cent of first births, more than twice the figure 20 years ago.

Peter Nagy, of Reproductive Biology Associates in Atlanta, who led the study, said: “What is frightening is that if we think of our parents, most of them were relatively young when we were born. Today society is changing . . . We are likely to see more fertility problems.”

Any such effect could be heightened by the growing popularity of a fertility technique known as intra-cytoplasmic sperm injection, or ICSI, which was developed to treat male infertility and now accounts for about half of all procedures. Because ICSI involves injecting an egg with a single sperm, which might not otherwise have been capable of fertilising it, concerns have arisen that boys born in this way could also grow up to be infertile.

It has long been understood that the quality of a woman’s eggs deteriorates as she approaches the menopause, causing a sharp decline in her fertility after the age of about 35.

Dr Nagy asked female IVF patients how old their mothers were when they were born, and at what age they went through the menopause. This allowed him to calculate the “biological age” of the mothers’ ovaries, by comparing age at menopause with the age at which their daughters were born.

He found that the women were more likely to become pregnant if they were born to relatively young mothers, suggesting that being born to an older mother has a negative impact on fertility.

“I believe the correct conclusion is that maternal age and reproductive age is an important determining factor not only for the patient herself, but also determines to a certain extent the chances for her daughters,” he told the American Society for Reproductive Medicine conference in New Orleans yesterday.

“For every year of increase in age, it could be more difficult for the daughter.”

Professor Bill Ledger, of Sheffield University, said that the study raised genuine concerns. “There are drawbacks to being the child of an older egg. It’s another piece of evidence for people to consider when they choose not to have children at the peak of reproductive life, between the ages of 20 and 35.”

• Some infertile women could improve their chances of having children by taking multivitamin tablets at least six times a week to protect against failure to ovulate, according to a Harvard Medical School study of 18,000 nurses over eight years.

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