How Long Is a Full-Term Pregnancy?

Pregnancy is generally thought to last 40 weeks, although how long a woman can be pregnant can vary. In the past, full-term was used to describe pregnancy that lasted from three weeks before the due date to three weeks after (approximately 37–42 weeks).

In late 2012, it was recognized that babies born at different times during that five-week window had varying outcomes and challenges, so the working definition of “full-term” was modified, with an official statement from the American College of Obstetricians and Gynecologists (ACOG) put out in 2013. A baby’s lungs, liver, and brain continue to develop during those last weeks of pregnancy, so it’s important to take that into account.

Term Levels

The new definition of “full-term” actually breaks “term” into various levels.

Early-term is defined as 37 weeks through 38 weeks and six days. Full-term is 39 weeks through 40 weeks and six days. Late-term is 41 weeks through 41 weeks and six days. The post-term is 42 weeks and after.

While women carrying multiples or those with other high-risk pregnancies might be advised to deliver before full-term, it is generally advised to let your pregnancy unfold naturally and not request induction prior to being full-term.

Birth Statistics in the U.S.

In 2017, the overall United States preterm birth rate rose 1 percent to 9.93 percent of all births, according to the Centers for Disease Control and Prevention (CDC). In this case, preterm birth refers to births before 37 weeks gestation.

It can be hard to find information on births that are “early term” because they are still a term, and not really “premature,” per se. While these babies might face more interventions, they aren't technically premature and this data isn't as readily available.

More and more, women are being urged not to electively schedule induction or birth before 39 weeks, if possible. If you’re concerned about the statistics, ask your doctor what her practice’s birth statistics are. This will give you a good idea of how she and her coworkers approach pregnancy and birth.

Why Is Full-Term Important?

Especially if you’re scheduling an induction or Cesarean section, waiting until at least 39 weeks of gestation can greatly improve outcomes for your baby. According to the March of Dimes, waiting until 39 weeks of gestation can help ensure full development of the brain, lungs, and liver. It also reduces the likelihood of vision and hearing problems, gives the baby time to gain sufficient weight, and promotes being able to suck, swallow, and stay awake after birth long enough to eat.

Sometimes, doctors will induce early, like in the instance of twins, or if there are serious health reasons that necessitate the birth of the baby. Scheduling an induction to try to avoid a “big baby” or because you want the baby born around a certain time can have serious consequences.

Sometimes, your due date can be wrong by as much as two weeks, even with ultrasound, especially if your period was irregular. By allowing your body to go into labor naturally, as close to 39 or 40 weeks as possible, you reduce many risks that accompany a preterm birth.

If you’re concerned about your ability to go full-term for your pregnancy, or if you're worried about having an early-term baby, talk with your obstetrician or midwife. She will be able to go over all of the health risks and things to watch out for if your baby is born early, and what will happen if you give birth pre-term.

Your doctor knows you, your medical history, and what’s been going on with your pregnancy, and she’ll be able to provide you with personalized advice and guidance to help ease your worries and plan for a healthy birth. While going full-term is the ideal, many women do give birth to healthy babies preterm.