When Is The Baby Due? It's Complicated

While intellectually, most expectant mom's understand that the due date is only accurate within an up to two week window, folks still want to know a specific estimated time of arrival. Now from Medpagetoday.com comes news of this research, concluding that mom's may do better with a range of dates.

... 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."

Here's what I've learned from my patients - nobody seems to worry if the baby arrives a week early. But one or two days late is quite a different story. There's also evidence to suggest that the medical equivalent of eviction proceedings aka induction of labor at 41 weeks results in fewer Cesareans and better perinatal outcomes than just waiting. Of course you won't know when 41 weeks is reached unless you know a due date.

Finally, as I tell my patients, due dates are like train schedules. Just because the train is expected doesn't mean that's when it pulls into the station.