Type O blood may be fertility barrier

A woman's blood group could influence her chances of getting pregnant, scientists claim. Women with blood type O may struggle to conceive, they said, due to a lower egg count and poorer egg quality, according to a study. Women with blood group A seem to be better protected against falling egg counts.

The finding could prompt experts to look more closely at a woman's blood group when charting her fertility. More than 560 women, with an average age of 35, who were undergoing fertility treatment took part in the research, led by experts from Albert Einstein College of Medicine in New York and Yale University.

Blood samples were taken to measure levels of follicle-stimulating hormone (FSH), a well-known marker of fertility. FSH levels greater than 10 suggest a woman will have more difficulty conceiving than those whose levels are under 10. A high FSH level indicates a diminished ovarian reserve, which refers to both egg quality and the number of eggs left available for fertilisation. The ovarian reserve tends to decline significantly as a woman reaches her mid and late 30s and faster in the early 40s.

The study found that women with blood type O were twice as likely to have an FSH level greater than 10 as those in any other blood group. The findings held true even when a woman's age was taken into account, and the fact the women came from two different clinics.

Those with blood group A were "significantly less likely" to have an FSH level greater than 10 than those who were blood group O. Some 44 per cent of the UK population are blood group O and 42 per cent are type A. People with blood group A carry the A antigen, which is a protein on the surface of the cell, but this is absent in people with O type.

Dr Edward Nejat, from the department of obstetrics and gynaecology at Albert Einstein College, said FSH levels were just one marker of fertility and more studies were needed. "A woman's age remains the most important factor in determining her success of conceiving. The baseline FSH gives us an idea of the quality and quantity of a woman's eggs."