What is full term?

To help more babies be born healthy, the American College of Obstetricians and Gynecologists (ACOG) and the Society for Maternal-Fetal Medicine (SMFM) recently changed the way they define births that happen after 37 weeks of pregnancy.

Pregnancy usually lasts about 40 weeks (280 days) from the first day of your last menstrual period (also called LMP) to your due date. Your due date is the date that your provider thinks you will have your baby.

ACOG and SMFM now define a full-term pregnancy as a pregnancy that lasts between 39 weeks, 0 days and 40 weeks 6 days. Babies born full term have the best chance of being healthy, compared with babies born earlier or later.

What are the new definitions?

The definitions are:

  • Early term: Your baby is born between 37 weeks, 0 days and 38 weeks, 6 days.
  • Full term: Your baby is born between 39 weeks, 0 days and 40 weeks, 6 days.
  • Late term: Your baby is born between 41 weeks, 0 days and 41 weeks, 6 days.
  • Postterm: Your baby is born after 42 weeks, 0 days.

Why did the definitions change?

In the past, a pregnancy that lasted anywhere between 37 to 42 weeks was called a term pregnancy. Health care providers once thought this 5-week period was a safe time for most babies to be born.

But new research shows that every week of pregnancy counts for the health of your baby. Lots of important things happen to your baby in the last few weeks of pregnancy. For example, your baby's brain and lungs are still developing. Being pregnant for at least 39 weeks gives your baby’s body the time it needs to grow and develop.

The new definitions can help more babies be born healthy by helping to prevent births that are being scheduled a little early for non-medical reasons. If your pregnancy is healthy, wait for labor to begin on its own.

See also: Why at least 39 weeks is best for your baby, Infographic: Healthy babies are worth the wait (.PDF, 707KB)

Last reviewed: October, 2013