Natural Variations in Pregnancy Length

A new study out of the U.K. suggests that the length of pregnancy naturally varies between different women by as much as five weeks. Although it has always been known that human pregnancies last between 37 and 42 weeks, the variation has previously been attributed to imperfect methods of estimating due dates.

In the new study, researchers from the National Institute of Environmental Health Sciences were able to pinpoint the actual day that women became pregnancy by taking daily urine samples. In the study group of 125 women it was found that the length of pregnancy varied by as much as 37 days! It is thought that length of pregnancy is affected by a number of factors including a woman's age and weight at birth.

The finding suggests that while due dates are useful estimates, it is important to remember that every woman is different. In particular, practitioners should be cautious about intervening too early in a pregnancy.

This might also provide a sigh of relief for all the pregnant women who remain pregnant past their due date. Now when you get the dreaded "when are you due" question, you can answer, "XX date, but due to natural human variation it could be next week or the week after."

*Results from the study are published in the journal Human Reproduction