What is a post-term pregnancy?

A pregnancy that lasts more than 42 weeks is called post-term. A pregnancy that is between 41 and 42 weeks is called late-term. Most women deliver between 37 and 42 weeks of pregnancy.

What causes post-term pregnancy?

Healthcare providers don't know why some women carry a pregnancy longer than others. It's often because of miscalculating the due date. You are also more likely to have a post-term pregnancy if you:

• Are pregnant with your first baby

• Had past pregnancies that went past 42 weeks

• Are overweight

• Are having a boy

What are the symptoms of post-term pregnancy?

There are no symptoms of a post-term pregnancy. 

How is post-term pregnancy diagnosed?

To calculate your due date, your healthcare provider will:

• Measure the size of your uterus at certain points in early pregnancy

• Note the date they first hear your developing baby's heartbeat

• Note when you first feel your baby moving in your uterus

• Use ultrasound

In a post-term pregnancy, your healthcare provider may do testing to check on your baby's well-being and for problems. Tests may include:

• Ultrasound

• Seeing how your baby's heart rate responds to activity

• Checking the amount of amniotic fluid

How is post-term pregnancy treated?

The goal is to prevent problems and deliver a healthy baby. Your healthcare provider will base specific treatment on your pregnancy, age, and general health. It will also depend on how bad the condition is.

Your healthcare provider may do maternal and fetal testing to watch for problems. Tests include:

• Fetal movement counting. This keeps track of your baby's kicks and movements. A change in the number or frequency may mean the developing baby is under stress.

• Nonstress testing. This test watches how your baby's heart rate increases with your baby's movements. This is a sign of your baby's well-being.

• Biophysical profile. This test combines the nonstress test with an ultrasound to look at your baby's well-being.

• Ultrasound. This test uses high-frequency sound waves and a computer to make images of blood vessels, tissues, and organs. Ultrasounds are also used to follow the growth of your developing baby.

• Doppler flow studies. This is a type of ultrasound that uses sound waves to measure blood flow. The test is commonly used if a developing baby is not growing normally.

If tests find that it is not healthy for the developing baby to stay in your uterus, your healthcare provider may start labor to deliver the baby. Your healthcare provider will talk with you about the decision to start labor.

Once labor begins, your provider will keep track of your baby's heart rate with an electronic monitor. This is done to watch for changes in the heart rate caused by low oxygen levels. You may need a cesarean delivery if your baby's condition changes.

Amnioinfusion is sometimes used during labor if there is very little amniotic fluid or if the baby is pressing on the umbilical cord. A sterile fluid is put into the uterus with a hollow tube (catheter). The fluid helps replace the amniotic fluid and cushions the baby and cord.

What are possible complications of a post-term pregnancy?

Women with post-term pregnancy, especially with a large baby, are more likely to have:

• Longer labor

• Forceps or vacuum-assisted birth

• Vaginal tearing or injury

• Cesarean delivery

• Infection, wound complications, and bleeding after birth

There are also risks for the unborn and newborn baby in a post-term pregnancy. These include:

• Stillbirth and newborn death

• Placenta problems

• Decreased amniotic fluid

• Baby may stop gaining weight, or may even lose weight

• Birth injury if the baby is large

• Baby breathes in fluid containing the first stool (meconium aspiration)

• Low blood sugar (hypoglycemia) because the baby has too little glucose stored

When should I call my healthcare provider?

Once your pregnancy has reached 37 weeks, you'll have weekly appointments with your healthcare provider. If your pregnancy goes past 41 weeks, you and your healthcare provider will talk about your choices. You will also decide how often you need to be seen to check your pregnancy and the health of your baby. It is important to keep all of your appointments.

Contact your healthcare provider right away if:

• Your membranes rupture and amniotic fluid comes out

• You have bleeding

• You notice a change in your baby's activity level

Key points about post-term pregnancy

• A pregnancy that lasts more than 42 weeks is called post-term.

• Healthcare providers don't know why some women carry a pregnancy longer than others.

• You may need tests to watch for signs of problems.

• If tests find that it's no longer healthy for your baby to stay in your uterus, your healthcare provider may start labor to deliver the baby.

Next steps

Tips to help you get the most from a visit to your healthcare provider:

• Know the reason for your visit and what you want to happen.

• Before your visit, write down questions you want answered.

• Bring someone with you to help you ask questions and remember what your provider tells you.

• At the visit, write down the name of a new diagnosis and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you.

• Know why a new medicine or treatment is prescribed and how it will help you. Also know what the side effects are.

• Ask if your condition can be treated in other ways.

• Know why a test or procedure is recommended and what the results could mean.

• Know what to expect if you do not take the medicine or have the test or procedure.

• If you have a follow-up appointment, write down the date, time, and purpose for that visit.

• Know how you can contact your provider if you have questions, especially after office hours or on weekends.