The trend to delay childbirth by women seeking to build careers before starting a family could provoke a fertility crisis in the next generation, research suggests.
For the first time, scientists have shown ageing not only reduces a woman's chances of becoming pregnant - it may also reduce her daughter's chances.
A study of women attending an infertility clinic found that those who failed to become pregnant had older mothers than those for whom treatment was successful and led to the birth of a baby.
Peter Nagy, the head of Reproductive Biology Associates, a fertility clinic in Atlanta, who led the study, said: "What is frightening is our parents mostly were young [when they had children]. But today society is changing and a lot of women are delaying childbirth. What we will see in 20 to 30 years' time will be completely different. It means [delay] is a problem not only for the woman, but for her daughter. It will add to pressure on women."
Dr Nagy added that it was the first time research had indicated that a woman's age at the time she gave birth could influence the chances of reproduction in the next generation.
"We all know the age of a woman is very strongly correlated with her chance of a healthy pregnancy and of having a baby. If a woman is 25 her chances of getting pregnant are perhaps 90 per cent, and if she is 40 her chances may be 10 per cent. That is because her ovaries and eggs are ageing and fertility declines with age.
"The scientific question is: if a 40-year-old gets pregnant and has a baby [daughter], will that baby, when she grows up, have exactly the same chance of getting pregnant as if her mother had been 25?" he said.
To answer the question, the researchers asked 74 women going for fertility treatment at the clinic what age their mother was when they were born. The results showed that the mothers of those who achieved a pregnancy after treatment were 2.5 years younger when they had their daughters (average age 25.7 years) than the mothers of daughters who failed to become pregnant (average age 28.2 years).
A much more marked difference was observed when the researchers looked at the biological age of the mothers - calculated from the age at which they reached menopause. That showed that mothers of the successfully treated daughters gave birth to them on average almost five years earlier - 24.7 years before they reached the menopause - than the mothers of those whose treatment was unsuccessful (19.6 years).
Dr Nagy said: "The pregnant group were born five years younger in terms of ovary age. The results demonstrate maternal age at childbirth - relative to the menopause - is an important reproductive factor."Reuse content