Understanding Due Dates and Pregnancy Length

The maternity team at Gainesville's All About Women discuss due dates and how long you can really expect to be pregnant

It is perhaps the most angst-filled question of pregnancy: “When is my baby going to come?” Not only are you excited to meet your new baby, but so is everyone else, and they all want to know when your due date is. And though you may tell yourself that the due date doesn't matter, expecting moms can often put a lot of subconscious pressure on a particular date.

So let's take a few minutes and talk about the true length of pregnancy and what you can expect for your "due date."

Pregnancy Length Average

An average pregnancy lasts 40 weeks from the first day of the last menstrual period (LMP). Using this date, an OB-GYN can calculate a woman's estimated date of delivery (EDD). But it is important to understand that an EDD is simply that, an estimated date. The ACOG acknowledges that the actual length of a pregnancy can vary greatly from woman to woman, and from pregnancy to pregnancy.

In fact, only 5% of women have their baby on their predicted due date. That's because 40 weeks of pregnancy is an average. In real life, one woman's pregnancy may last 37 weeks while another's lasts 41. That's a difference of a whole month!

Pregnancy Length Range

Of course, as you grow more and more uncomfortable you may be tempted to ask your OB-GYN about induction. But your provider may recommend that you wait, especially if it's still fairly early. While doctors use to consider a pregnancy full term at 37 weeks until fairly recently, new research and the following recommendations have changed the definition of full term to over 39 weeks.

Here's how obstetricians now classify pregnancy lengths:

Early Term: Between 37 and 38 weeks
Full Term: Between 39 Weeks and 40 weeks, 6 days

Late Term Between 41 weeks and 41 weeks, 6 days
Postterm: 42 weeks and beyond

If you're before the 39-week mark, inducing labor or scheduling a C-section isn't recommended unless you have a specific condition such as preeclampsia or placenta previa in which your obstetrician deems early delivery the safest option for you and baby.

Baby Development in the Last Weeks of Pregnancy

If you feel a little cross that you might be pregnant for 41 weeks, just remember that the last few weeks of pregnancy are pivotal for your baby's development. Their lungs, immune system and brain are all still developing up until the day of delivery. Medical researchers found that babies born before 39 weeks are at higher risk for admission to the NICU because of the following possible complications:

Hypoglycemia (low blood sugar)
Needed respiratory support or mechanical ventilation or intubation
Need for IV fluids or antibiotics

Furthermore, early term babies delivered by C-section were at higher risk (12%) for admission to the NICU and for complications following delivery compared to full term babies delivered by C-Section. On the flipside, risks for babies start increasing if your pregnancy goes postterm —which is more than 42 weeks— so your doctor may recommend induction as you near the 42-week marker.

So When's My Due Date?

The short story is that there is definitely rarely such thing as a "due date." You might want to consider just telling people the month you're hoping for baby to come, or take your EDD and add two weeks for a fairly safe bet of a date by which baby should have arrived. Of course, you definitely want to have your hospital ready by week 37 just in case!

At All About Women, our obstetricians and midwives are here to help you through birth, no matter what pregnancy and labor throw your way. Continue getting ready for the big day by reading our articles about pain relief during labor and recognizing Braxton Hicks contractions.