The lead author, Dr Edward Nejat, of the department of obstetrics and gynaecology at the Albert Einstein College of Medicine in New York, said his findings were based on women having fertility treatment at the Yale University and the Montefiore Institute in New York.

Fertility experts regard a high FSH level as a key indicator of having a low egg count. FSH is produced by the body to stimulate the follicles in the ovaries that produce eggs.

The study of 560 women, whose average age was just under 35, found that those with blood type O were more likely to have higher levels of "follicle stimulating hormone" (FSH) than those with type A.

Researchers who tested a group of women seeking fertility treatment found those with the blood type O appeared to have a lower egg count and poorer egg quality than others. By contrast those with blood type A seemed to have more and better quality eggs.

A study suggests that a woman's blood group could influence her chances of getting pregnant.

The findings could lead to women with type O blood being advised to try for a baby earlier, but experts said more research was needed before such a step was taken.

As a woman's ovaries run out of eggs in her 30s and 40s, production therefore has to be stepped up to encourage more eggs. The presence of high levels of FSH indicates lower numbers of eggs.

The study found that women with blood type O were twice as likely to have an FSH level above 10 as those in any other blood group.

People with blood group A carry the A antigen, a protein on the cell surface, that is absent in people with O type.