'Heart risk' of babies born to women in their forties

The warning comes in a report laying out the health dangers relating to women who delay motherhood, a growing trend.

The five-year study of eight million births also says that over-30s who become pregnant are four times more likely to suffer from high blood pressure and twice as likely to develop diabetes - both of which can be harmful to their babies.

Despite such risks, almost half of the 720,000 births each year are to women aged 30 or above, while the birth rate for over-45s has doubled in a decade with 1,177 babies born in 2005.

The study, published in the journal Human Reproduction, reveals mothers over 45 are three times more likely to have a Caesarean than those in their early 30s, and twice as likely to give birth prematurely.

Babies born during the procedure are twice as likely to die in the first month and premature babies within the first weeks of life.

One in ten born before 37 weeks develops a permanent disability such as lung disease, cerebral palsy, blindness or deafness.

The research, which involved U.S. mothers, was carried out at the University of Miami.

Last night, IVF expert Geeta Nargund, head of reproductive medicine at St George's Hospital in London, said it was important women were made aware of the risks of putting off motherhood.

She said for many women, pregnancy late in life was something they were forced into because of working or financial circumstances.

"A lot of women we see in their early 40s never thought they would end up in a fertility clinic," she added.

"There are a lot of social factors involved. As a nation, we have to address the socio-economic factors that lead to women leaving it too late."