Key Points
Pregnancy usually lasts about 40 weeks from the first day of your last menstrual period to your due date.
A full term pregnancy lasts between 39 weeks, 0 days and 40 weeks, 6 days. This is 1 week before your due date to 1 week after your due date.
Every week of pregnancy counts for your baby’s health. For example, your baby’s brain and lungs are still developing in the last weeks of pregnancy.
If your pregnancy is healthy, wait for labor to begin on its own.
What is a full-term 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.
The American College of Obstetricians and Gynecologists (also called ACOG) and the Society for Maternal-Fetal Medicine (also called SMFM) define a full-term pregnancy as a pregnancy that lasts between 39 weeks, 0 days and 40 weeks 6 days. This means your pregnancy lasts between 1 week before your due date and 1 week after your due date. Babies born full term have the best chance of being healthy, compared with babies born earlier or later.
ACOG and SMFM use these definitions to describe term pregnancies:
- 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.
How was the length of pregnancy defined in the past?
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. In 2013, ACOG and SMFM updated the definitions for term pregnancies because 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.
These 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.
Last reviewed: September, 2018
See also: Pregnancy week by week feature, 39 weeks infographic, Why at least 39 weeks is best for your baby
