A woman's ability to conceive in early middle age may be influenced by her blood type

A study of 560 women undergoing fertility treatment found that those with type "O" blood had chemical signs linked to low egg numbers. Approximately 44% of the British population has type "O" blood. The researchers looked at the levels of a chemical called follicle-stimulating hormone (FSH) in the women, who had an average age of 35. A woman has a fixed number of eggs, her "ovarian reserve", which are released gradually over her fertile life. High levels of FSH are thought to be an indicator that this reserve is diminishing more quickly - which can reduce chances of conception once a woman reaches her 30s and 40s. Analysis of blood samples revealed that the women with type "O" blood were more likely to have higher FSH readings. Those with type "A" blood - the other major blood group in Britain - had lower FSH levels.