A new study suggests that the length of a woman's menstrual cycles can indicate her ability to conceive.

Researchers at Emory University in Atlanta found women with cycles lasting 30 to 31 days were most likely to get pregnant.

But women whose cycles were shorter or longer than that were three times more likely to miscarry.

The study of nearly 500 women, published in the January issue of the journal Epidemiology, also found that women whose periods lasted five days were among those who conceived the most.

In the study, women completed daily diaries with information on menstrual bleeding, intercourse, birth control use and other factors.

During each menstrual cycle, women collected at least two urine samples, which were analyzed for hormones to detect early pregnancies. Women were followed for a year or until the end of pregnancy.

• Study Abstract