Pregnancy Beyond 42 Weeks

What is the concern about pregnancy that lasts longer than 42 weeks?

A normal term pregnancy lasts 37 to 40 weeks from the first day of your last menstrual period. When a pregnancy lasts longer than 40 weeks, the placenta may no longer be able to bring enough oxygen and nutrients to the baby. This is called a postterm pregnancy.

The chances of a problem for the baby slowly start to increase after 40 weeks and get much higher after 42 weeks. Examples of risks to the baby include:

  • Your baby may not get enough oxygen or nutrients from the placenta. This could stop your baby’s growth or harm your baby’s brain. It might even cause death.
  • Your baby may have a bowel movement inside the uterus. If this happens in the amniotic fluid before birth, your baby may breathe it into the lungs. This could cause serious breathing problems after birth.
  • Less amniotic fluid around the baby may make labor more stressful for your baby.
  • Your baby may have low blood sugar.

What is the cause?

It is not known why some pregnancies last longer than 40 weeks.

How is it diagnosed?

You and your healthcare provider must first accurately date your pregnancy. Your healthcare provider uses several kinds of information to calculate the due date, including the date of your last menstrual period and how regular your periods are. An early exam of your uterus and an early positive pregnancy test can help check your baby’s age and due date. Ultrasound can be used to confirm your baby’s age. An ultrasound uses sound waves to show pictures of your baby. Your baby can be measured with ultrasound as early as 5 or 6 weeks after your last menstrual period. This method is most accurate in the first half of your pregnancy.

There are several ways to check your baby’s health, such as:

  • A kick count, which is counting your baby’s movements during a certain length of time. A healthy baby usually moves at least 10 times in 2 hours. Count each kick, roll, swish, or flutter as 1 movement.
  • A nonstress test, which uses a monitor strapped your belly to record how your baby’s heart rate changes when your baby moves
  • A biophysical profile, which uses sound waves (ultrasound) along with a nonstress test to check your baby’s breathing, movement, heart rate and muscle tone and the amount of fluid around the baby
  • A contraction stress test, which uses a monitor strapped to your belly to record how your baby’s heart rate changes after you are given medicine to cause contractions

How is it treated?

Information from the tests helps your healthcare provider determine the best treatment.

  • If the baby appears to be healthy and not in danger, and your health is good, your provider may check you regularly while you wait for labor to begin.
  • If you have passed your due date, your healthcare provider may consider inducing labor as your pregnancy nears 41 to 42 weeks. However, there are also risks if your baby is delivered before it is ready to be born. Also, you could have problems during labor, such as prolonged labor and infection. In this case, you might need to have a C-section (a surgery that delivers your baby through a cut in your belly and uterus).

Your healthcare provider will talk about your choices for treatment and explain any risks.

Developed by RelayHealth.
Adult Advisor 2015.1 published by RelayHealth.
Last modified: 2014-05-08
Last reviewed: 2014-07-03
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
Copyright ©1986-2015 McKesson Corporation and/or one of its subsidiaries. All rights reserved.

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