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What is considered full-term pregnancy? And why does delivery timing matter?

What is considered full-term pregnancy? And why does delivery timing matter?

5 min read

​​Pregnancy can be an exciting and often stressful time in life. In preparing for this huge life change, one thing you can get familiar with in advance is how your doctor might refer to your developing pregnancy and your gestational stage. One phrase you might hear? "Full-term" pregnancy.

In this article, we'll explain this newer terminology and why experts recently expanded the term nomenclature with new definitions. If you’re in a rush to get to the main takeaways, here they are up front:

  • A full-term pregnancy is a pregnancy carried for about 39 to 40 completed weeks since your last menstrual period (LMP). This time frame allows for full development of the fetus and increases the chances of healthy outcomes.
  • Experts used to only differentiate "preterm" from "term" pregnancies (before 37 weeks and after 37 weeks). New research showed that babies born at 39 weeks of gestation fare better than babies born at 37 weeks, so they redefined what “term” meant and classified "full-term" as the ideal time period for birth.
  • Doctors use "full-term" as a guideline for when a pregnancy is far along enough to safely induce delivery for elective reasons (meaning not for medical reasons). Think of it more as a medical framework rather than something you need to pay close attention to.
  • Unless you're inducing delivery or scheduling a cesarean section (C-section), there's no way to completely control when birth happens. The most important thing to do is to maintain healthy habits during your pregnancy.

“The vast majority of babies born after 37 weeks will do just fine and not need to go to the neonatal intensive care unit (NICU),” says Dr. Jenn Conti, MD, MS, MSc, OB-GYN and Modern Fertility medical advisor. “What this newer information has done is encourage the medical community to not electively induce labor before 39 weeks."

What is considered “full-term” pregnancy?

A pregnancy is "full-term" if a fetus grows inside the uterus for 39 to 40 completed weeks after your last menstrual period (LMP). That 39-40 weeks provides enough time for the fetus to fully develop (see a stage-by-stage breakdown here) and have the lowest chance of needing additional support to breathe, control its temperature, and control its blood sugar outside of the uterus. But this hasn't always been doctors' definition of term pregnancy.

According to the American College of Obstetricians and Gynecologists (ACOG), doctors were initially taught that 37-42 weeks marked a term pregnancy. Until very recently, there was only the distinction of “preterm” and “term” pregnancies. The issue with this binary definition was that there was a wider discrepancy between neonatal outcomes within those final five weeks of pregnancy — and it was difficult to predict one-size-fits-all outcomes for infants.  

Fast forward to 2012 when a group of OB-GYN experts further characterized exactly what happens in the last weeks of pregnancy. More research pointed to the idea that babies born before 39 weeks were more likely to have adverse outcomes (particularly in terms of lung development) when compared to babies born at 37 weeks. So, ACOG adjusted their guidelines, creating the idea of "full-term" pregnancy at 39 weeks.

Why does dating terminology matter in pregnancy?

While every week and trimester in pregnancy is important for development, delivery doesn't have to happen when you're exactly 40 weeks pregnant in order for a baby to be healthy. The language around "full-term" is more for your healthcare provider than it is for you.

"Babies come on their own all the time before 39 weeks," explains Dr. Conti. "We use the definition of 'full-term' as a guideline for when to allow elective inductions of labor only." In other words, how "term" your pregnancy is (early term/preterm, full-term, postterm) helps your healthcare provider determine when they may or may not recommend induction of labor for non-medical reasons.

Is there anything you can do to influence when you deliver?

Unless you're inducing delivery (either electively after 39 weeks or at any gestational age for a medical indication) or scheduling a cesarean section (C-section), there's no way to know with certainty when your delivery will happen — and there's no way to completely control it (research shows that genetics may even play a role).

What is under your control is working toward a healthy lifestyle during pregnancy:

  • Take a prenatal vitamin with folate: Starting a prenatal vitamin with folate at least one month before conception through pregnancy supports healthy fetal neural tube (brain and spine) development.* Even though your prenatal might have a lot of the nutrients your body needs, it's also important to eat balanced, nutritious meals during pregnancy.
  • Know what foods to stay away from: Unpasteurized cheese, uncooked meats, and unwashed produce can all have the bacteria Listeria and pregnant people are 10 times more likely to develop an infection from it (which can be passed on to the fetus).
  • Get in regular exercise: Exercise during pregnancy is recommended. Try for at least 30 minutes of moderate-intensity exercise a day (think of a brisk walk).
  • Abstain from alcohol, cigarettes, and moderate your caffeine intake: Medical guidelines are clear that alcohol and cigarettes are a no-go during pregnancy. But caffeine is okay in moderation — just cap it at 200 mg a day.

“It’s also super important to talk to your healthcare provider about your mental health,” says Dr. Conti. “Pregnancy and the postpartum are times when hormones, changing family and financial dynamics, and other life stressors can all influence how you’re feeling mentally — and having a strong support system is vital. One of my absolute favorite resources for patients is Postpartum Support International.

Does delivering before or after you're full-term mean your due date was "incorrect"?

No. Your estimated due date is the day your pregnancy turns 40 weeks. This date, which is calculated based on the first day of your last menstrual period (LMP), an early ultrasound, the date of IUI insemination, or of an IVF embryo transfer, helps your doctor check for developmental milestones — and identify if any issues arise.

But your due date is an estimate of when you should deliver: Only 5% of babies are delivered on their actual due date. What's more important than exact delivery age is whether or not fetal development is far enough along for an infant to be born without increased risk of health problems — that's where close attention to the gestational age and subdivisions of a "term" pregnancy factor in. If a delivery comes before or after you're full-term, that doesn't mean the due date was "incorrect" — it means you didn't deliver at 39 to 40 completed weeks.

The bottom line

A pregnancy is "full-term" if delivery happens between 39 and 40 completed weeks, when there's a decrease in the likelihood of adverse outcomes and health risks. But because delivery timing isn't fully within our control, the most important things to do are take steps to support a healthy pregnancy and make sure to attend all of your prenatal appointments so your healthcare provider can monitor you.

Always remember that your healthcare provider is there to answer any questions you have throughout your pregnancy. And if you're looking to connect with and get support from other pregnant people, our free online community has a dedicated channel you can request to join today.

This article was medically reviewed by Dr. Jennifer Conti, MD, MS, MSc.

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Jocelyn Solis-Moreira

Jocelyn Solis-Moreira is a health and science journalist focusing on research about medicine, public health, and women's health.

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