Older IVF mums have healthier newborns than women who conceive naturally after 40

A survey of more than 300,000 live births showed that women aged 40 or over who conceived naturally were more than twice as likely to have a child with birth defects than those of the same age who had undergone IVF.

The team from the University of Adelaide, who collated data from every live birth in South Australia between 1986 and 2002, have described the findings as "remarkable".

Prof Michael Davies, who led the research, said: "There is something occurring with women over the age of 40 who use assisted reproduction.

"There is some aspect of IVF treatment in particular that could be helping older women to redress the maternal age issues we see among natural conception, where we observe a transition at around the age of 35 towards a steadily increasing risk of birth defects.

"We don't know what that is quite yet. It could be an aspect of hormonal stimulation that helps reverse the age- related decline in control of ovulation."

Prof Davies said his findings could have significant implications for infertility treatment if researchers can understand why older women do better on assisted reproduction.

However, Yacoub Khalaf, a consultant gynaecologist at Guys and St Thomas' Hospitals in London, pointed out that, despite the size of the overall study, the number of births in the over-40 group was "relatively small".

He said Prof Davies' inferences could be the result of a statistical anomaly.

Jody Day, founder of Gateway Women, an online support network for women without children, said: "Many couples think that IVF is more successful than it actually is, and it comes as a real shock when it doesn't work. Knowing when to stop is very individual.

"It is an option that is rarely presented at infertility clinics, and is almost too taboo to even think about."