The Myth of the 40 week EDD

There are a few topics that get me pretty worked up when talking about pregnancy. One of them is people who get all riled up about a woman being "overdue" when they are actually just talking about a pregnancy that is post 40 weeks.

My husband has a PhD in a branch of physics and is a research scientist by trade. I only have a liberal arts bachelor's degree but several of my jobs prior to becoming a stay at home wife and mom included medical and public health research. So when it came to our only child that we fought so hard to conceive, you'd better believe that we researched EVERYTHING.

Despite all my reading prior to even getting pregnant (I spent the first year of our infertility journey researching birth), I was still shocked to find out how much of current treatment of pregnant women is not at all backed up by research and in fact much of it is completely contradicted by research. The myth of the 40 week estimated due date is one of those things that is contradicted by research.

This article summarizes nicely the information in this research. Despite our best efforts, we were not able to find any evidence based research that backed up a 40 week estimated due date but we were able to find another study from Ultrasound in Obstetrics and Gynecology 1999; 14:23-28 that once again debunks the 40 week EDD.

You might think, "Okay, but why does this matter?" It matters because in my town women are told from their first OB appointment that it's not safe to go "overdue" and by "overdue" they mean 40 weeks. I'll talk about the safety of going postdate in another post. I'm sure that my town is not the only town in America where women are faced with a mythical line in the sand, in fact with a 1/3 c-section rate in this country, I'd say that my town is probably pretty typical. Recognizing a more accurate estimated due date won't solve all the problems of maternity care today but it is a step in the right direction.