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Reviewed by the Faculty of Harvard Medical School

Making the Last Weeks of Pregnancy Count

In recent years, more women are asking to schedule their vaginal deliveries (induction) or Cesarean sections before 39 completed weeks of pregnancy. (These are called elective deliveries.) A baby reaches full term at 40 weeks. Giving birth before a baby reaches full term can be harmful to you and your baby.

Your baby has the best chance of being born healthy if you schedule the birth after 39 weeks of pregnancy. This will give your baby's brain, lungs and other organs the time they need to develop fully. Babies born before 39 weeks gestation may have medical problems that need extra medical care. This means they may need to spend more time in the hospital or in the neonatal intensive care unit (NICU).

What is a full-term pregnancy?

A "full-term" pregnancy is one that lasts between 37 and 42 weeks. Although pregnancies that include the 37th and 38th weeks are considered "term" births, medical experts, including the American College of Obstetricians and Gynecologists (ACOG), strongly advise against an elective delivery before the end of 39 completed weeks of pregnancy. (An elective delivery means there is no medical reason requiring early delivery.)

How do I know when my baby is due?

Your due date is an estimated date of when the baby will be born. It is based on the average length of pregnancy — 280 days, or 40 weeks, from the first day of your last period. Click here to calculate your due date.

It is important to review this date with your health care professional so you know when your baby is due. This date can sometimes change based on irregular menstrual cycles and ultrasound findings.

What are the benefits of waiting until I reach 39 completed weeks?

Here's why it's best to wait:

  • Important organs, like the brain, lungs and liver, need time to develop. A baby's brain at 35 weeks weighs only 2/3 of what it will weigh at 39 to 40 weeks.
  • Infants born after 39 weeks are less likely to have hearing and vision problems.
  • There is more time to gain weight in the womb. Babies born at a healthy weight have an easier time staying warm than babies who are small.
  • Babies need to suck and swallow and stay awake long enough to eat after they are born. Babies born early sometimes can't do these things.
  • Infants born before 39 weeks have a greater chance of lung and breathing problems at birth.
  • Babies born before 39 weeks have a greater chance of being admitted into the NICU.

What should I ask my health care professional before I schedule my delivery?

  1. When is my baby due?
  2. How is my due date calculated?
  3. Why would my due date be change during my pregnancy?
  4. What are considered medical reasons to schedule a delivery before 39 completed weeks of gestation?
  5. What is the harm of scheduling my delivery before 39 completed weeks?
  6. Where can I find more information about the benefits waiting 39 completed weeks before I schedule a delivery?

To learn more about the benefits of waiting to deliver, visit the March of Dimes:

Why the Last Weeks of Pregnancy Count

Typical Pregnancy Is Now Only 39 Weeks

Induction by Request

Cesarean Birth by Request

Cesarean Sections May Be Contributing to the Rise in Late Preterm Births

Last updated November 17, 2010