Women with type O blood may have a more difficult time conceiving than those with other blood types, while women with blood type A have a relatively higher chance of getting pregnant, according to a study.

The study was conducted jointly by the Albert Einstein College of Medicine in New York and Yale University. The researchers studied the relationships between blood types and fertility rates of more than 560 women with an average age of 35 who were receiving infertility treatments.

The researchers divided the women into groups according to their blood types and compared their levels of follicle stimulating hormone, a widely-accepted marker of fertility. The higher the FSH, the lower the quality and quantity of fertile eggs. Women with an FSH level higher than 10 have a more difficult time becoming pregnant than those with a level under 10.

According to the study, women with type O blood were twice as likely to have an FSH level over 10 than those with other blood types. And only a small number of women with type A blood had an FSH level surpassing 10.

This is the first time a potential link between blood type and fertility has been identified. "But a woman's age remains the most important factor in determining her success of conceiving," the study's leader Dr. Edward Nejat said, adding that more research needs to be done.