Why is 39 weeks so important?

midwife measuring pregnancy bellyIf your pregnancy is healthy, it is 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 he needs to grow.

Why is 39 weeks so important?

Here’s why your baby needs 39 weeks:

  • Important organs, like his brain, lungs and liver, get the time they need to develop. 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 who are born too small.
  • Your baby will be able to feed better. Babies born early can sometimes have difficulties with 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!

Have questions? Email us at AskUs@marchofdimes.org.

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3 Responses to “Why is 39 weeks so important?”

  1. Sandy King Says:

    Hi,

    This is an interesting topic, but when it comes to babies – nothing goes as planned!

    I had contractions at 24 weeks and had to be rushed to the ER. I took oral medication to ease the contractions, but they were at the point of admitting me!

    My pregnancy was also very painful and my little one moved around so much it was hard to sleep, lie down, move around etc, etc.

    I carried my little girl to 36 weeks and I’m happy to say she’s perfectly healthy – and still a little ball of energy!

  2. Mary Says:

    As a very experienced maternity nurse, it remains upsetting to see a healthy pregnant woman complain about the normal symptoms of pregnancy just to get induced…..electively. Taking care of a baby that is only 37 weeks is very difficult. Just because the mother was “tired of being pregnant” and continued to call the doctor asking for delivery, this late preterm baby has great difficulties. These babies, less then 39 weeks do not breast feed well. They do not stay warm. They have a higher admission rates to the Intensive Care Unit. These early babies have many sticks for blood work because they are too early. They have to be monitored more closely. PLEASE, do not request an induction. PLEASE do not request a C-section. Of course, if medically indicated, the healthcare provider will ensure a safe delivery but only if indicated. And also, C-section mothers have greater risk of bleeding from the uterus caused by the scars left behind from the surgery. Women are dying from bleeding after repeat C-sections. PLEASE, let nature work. PLEASE…..for your safety and your FULL-TERM baby’s safety listen to the March of Dimes!! PLEASE.

  3. Lori Kennedy Says:

    It’s also important to highlight the risks of waiting TOO long to induce. Our otherwise perfectly healthy daughter was stillborn at 40+ weeks.

    We had not heard about risks of letting a baby gestate for too long and I am hoping that is something the research and communications can focus on next.

    There are definite risks (that we had never heard of) that contributed to our daughter’s death: placenta starts to decline at some point, there is more time for accidents (cord accidents)…

    There is an optimal period for birth… not too early, not too late. Let’s move the conversation to include the risks of post-term birth, as well.

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