oh, baby!(Brief Article)

If you're trying to get pregnant, your calendar is probably filled with all sorts of dates and times. But is your "fertility window" as predictable as you think? Not necessarily, say researchers at the National Institute of Environmental Health Sciences (NIEHS) in Durham, N.C.

Traditional wisdom holds that there are six days in the middle of the menstrual cycle when intercourse can result in pregnancy. Yet a new study, published in the British Medical Journal, found that late ovulation was a common occurrence and that some women are actually fertile throughout their entire menstrual cycle.

Researchers analyzed daily urine samples from 213 healthy women ages 25 to 35, who were planning to get pregnant. The participants also kept a diary that included, among other information, when and how often they had sex. Lead researcher Allen J. Wilcox, M.D., noted that it took several years to analyze the 30,000 urine samples and diaries.

"In one sense," says Wilcox, "what we're describing is how much variability there is in individual women--how long the cycle lasts and when ovulation occurs." In the case ...