Why is 39 weeks so important?

January 17, 2022

Scheduling your baby’s birth means you and your health care provider decide when to have your baby. This can happy by inducing labor or cesarean birth  (c-section) instead of waiting for labor to begin on its own. However, if your pregnancy is healthy, it’s best to wait for labor to begin on its own. And if you do decide to induce labor, ask your provider if you can wait until at least 39 weeks.

Most people think that pregnancy lasts 9 months. But that isn’t exactly true. Pregnancy usually lasts about 40 weeks (280 days) from the first day of your last menstrual period (also called LMP) to your due date. A first-trimester ultrasound can also help to determine your due date.

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 experts now know that scheduling your baby’s birth a little early for non-medical reasons can cause problems for both mom and baby. Getting to at least 39 weeks gives your baby the time they need to grow.

Why are 39 weeks so important?

Here’s why your baby needs 39 weeks:

  • Important organs, like the brain, lungs and liver, get the time they need to develop. For example, at 35 weeks, a baby’s brain weighs just two-thirds of what it does at 39 weeks.
  • There is more time to gain weight. Babies born at a healthy weight have an easier time staying warm than babies born too small.
  • Your baby will be able to feed better. Babies born early can sometimes have difficulties sucking, swallowing, and staying awake long enough to eat.
  • Your baby is less likely to have vision and hearing problems after birth.

Why can scheduling an early birth cause problems?

There are some risks associated with inducing labor:

  • Your due date may not be exactly right. Even with an ultrasound, your due date can be off by as much as 2 weeks. If you schedule an induction and your due date is wrong, your baby may be born too early.
  • Pitocin, the medication used to induce labor, can make contractions very strong and lower your baby’s heart rate.
  • You and your baby have a higher risk of infection if labor doesn’t begin soon after your water breaks.
  • If the medications used to induce labor do not work, you may need to have a c-section.

What if there are problems with your pregnancy?

You may not have a choice about when to have your baby. Your provider may need to induce labor to help keep you and your baby safe. If your provider does decide to induce labor for the health and safety of you and your baby, you can learn more about how labor is induced on our website.

Remember: If your pregnancy is healthy, it is best to let labor begin on its own. If you and your baby are healthy, and you and your provider decide to induce labor, make sure you wait until at least 39 weeks. Healthy babies are worth the wait!