The normal length of pregnancy is 37 to 41 weeks. Early term is from 37 weeks to 38 weeks and 6 days. Full term is 39 weeks to 40 weeks and 6 days. Late term is 41 weeks to 41 weeks and 6 days. Postmaturity (dysmaturity) is a word used to describe babies born after 42 weeks. Very few babies are born at 42 weeks or later. Other terms often used to describe these late births include post-term, postmaturity, prolonged pregnancy, and post-dates pregnancy.
Researchers don't know why some pregnancies last longer than others. Sometimes a mother's pregnancy due date is off because she is not sure of her last menstrual period. Getting the date wrong may mean the baby is born earlier or later than expected. Getting an ultrasound in the first trimester (the first 12 weeks) is the most accurate way to tell the date of pregnancy, unless the date of conception is specifically known, such as with in vitro fertilization.
Postmaturity is more likely to happen when a mother has had a post-term pregnancy before. After one post-term pregnancy, the risk of a second post-term birth increases by 2 to 3 times. Other, minor risk factors include:
- First pregnancy
- Male baby
- Older mother
- Obese mother
- Mother or father with personal history of postmaturity
- White mother
Each baby may show different symptoms of postmaturity. Some of those symptoms are:
- Dry, loose, peeling skin
- Overgrown nails
- Large amount of hair on the head
- Visible creases on palms and soles of feet
- Small amount of fat on the body
- Green, brown, or yellow coloring of skin from baby passing stool in the womb
- More alert and "wide-eyed"
Symptoms of postmaturity sometimes look like other health conditions. Make sure your child sees his or her healthcare provider for a diagnosis.
Your baby's healthcare provider will check:
- Your baby's physical appearance
- The length of your pregnancy
- How old your baby appears to be
Your healthcare provider will check your unborn baby's health and look for any problems. Tests may need to be done such as:
- Nonstress testing. This looks at how the fetal heart rate responds to fetal movement.
- Checking the amount of amniotic fluid
Your healthcare provider may decide to start your labor early, depending on several things. During labor, your baby's heart rate may be watched with an electronic monitor. This will help spot changes in the heart rate caused by low oxygen levels. Changes in your baby's condition may require a cesarean delivery.
Special care of the post-term baby may include:
- Checking for breathing problems caused by baby's breathing in fluid containing the first stools (meconium)
- Blood tests for low blood sugar
Post-term babies are born after the normal length of pregnancy. Because of this they may grow larger than full-term babies. This may be a problem during labor and delivery.
Also, because the placenta ages toward the end of pregnancy, it may not work as well as before. Concerns from placental aging include:
- Less amniotic fluid. This may stop the baby from gaining weight or may even cause weight loss.
- Poor oxygen supply. Babies who don't get enough oxygen may have problems during labor and delivery.
- Meconium aspiration. Babies who stay in the womb longer are more likely to breathe in fluid containing meconium.
- Hypoglycemia or low blood sugar. This happens when the baby has already used up his or her stores of glucose.
Knowing your due date is the best way to know if your baby may be post-term. Keep track of the first day of your menstrual period. This can help estimate a baby's due date. An ultrasound test early in pregnancy can also help your healthcare provider figure out your baby’s age by checking the baby’s size. Ultrasound is also a good way to check the placenta for signs of aging.
- Postmaturity is a word used to describe babies born after 42 weeks.
- Researchers don't know why some pregnancies last longer than others.
- Postmaturity is more likely to happen when a mother has had a post-term pregnancy before.
- Your healthcare provider may decide to start your labor early.
- An ultrasound test early in pregnancy can help your healthcare provider figure out your baby’s age by checking the baby’s size.
Tips to help you get the most from a visit to your child’s healthcare provider:
- Know the reason for the visit and what you want to happen.
- Before your visit, write down questions you want answered.
- 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 for your child.
- Know why a new medicine or treatment is prescribed and how it will help your child. Also know what the side effects are.
- Ask if your child’s 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 your child does not take the medicine or have the test or procedure.
- If your child has a follow-up appointment, write down the date, time, and purpose for that visit.
- Know how you can contact your child’s provider after office hours. This is important if your child becomes ill and you have questions or need advice.
May 31, 2018
Lockwood CJ. ACOG Guidelines: Management of Late-Term and Postterm Pregnancies. Obstetrics and Gynecology. 2014;124:390-6., Wang M. Common Questions About Late-Term and Postterm Pregnancy. American Family Physician. 2014;90(3):160-5., Postterm pregnancy.. UpToDate.
Lee, Kimberly G, MD, MSc, IBCLC ,Freeborn, Donna, PhD, CNM, FNP