Range of Due Dates Better for Expectant Moms

A cohort of pregnant mothers who were followed from conception to birth showed that, despite a median gestational period of 268 days, length of pregnancy varied by 37 days even after excluding mothers who gave birth preterm, according to Anne Marie Jukic, PhD, of the Epidemiology Branch of the National Institute of Environmental Health Sciences in Durham N.C., and colleagues.

Factors affecting length of pregnancy included length of time to conception, rate of progesterone rise, the mother’s age, birth weight, and length of pregnancy in previous births, they wrote online inHuman Reproduction.

The authors noted that despite an estimated pregnancy period of 280 days from the mother’s last menstrual period routinely assigned to mothers, only 4% of pregnancies fall on that date, while 70% occur within 10 days of that estimate “even when the date is estimated by ultrasound.”

The authors studied the length of gestation through a cohort of 125 spontaneously conceived pregnancies to examine potential predictors of pregnancy length, such as hormonal levels at the early stages of pregnancy.