What is a postdate pregnancy?
A normal, full-term pregnancy lasts 37 - 42 weeks from the first day of your last menstrual period. If a pregnancy goes beyond 42 weeks, it is called a postdate pregnancy. There are two types. The most common type occurs when the due date is not correct, and the pregnancy is mistakenly labeled as postdate. This can happen because it is hard to know the exact date you became pregnant. Less often, a pregnancy may truly go past 42 weeks and become postdate.
Postdate pregnancy happens in 3-12% of all pregnancies dated by the last menstrual period. When early ultrasound is used, the chance decreases to 1-2%.
What are the risks of a postdate pregnancy?
Most babies born postdate are healthy. In some, there are risks to the fetus and newborn baby. These risks include:
- The placenta may not work well.
- The amount of fluid around the baby may decrease. This may cause the umbilical cord to become compressed before or during labor.
- The fetus grows larger which may cause some problems with birthing the baby.
- The fetus may show signs of distress in labor.
- Because of postdate or distress, the fetus may pass its stool while still inside the mother. If this occurs, there is a risk that the baby may develop a severe, perhaps life-threatening illness (meconium aspiration syndrome).
- The fetus or newborn may have postmaturity syndrome. Babies with this syndrome can have loss of fat, wrinkled and peeling skin, long nails, low blood sugar, and are at risk of stillbirth.
- There may be a greater chance of cesarean birth. Cesarean births can increase risks to the mother, such as infection, bleeding, and a longer recovery time.
What tests can be used to assess my fetus as I approach postdate?
If you go beyond 41½ weeks, some tests are advised to assess your baby’s well-being. These tests are based upon the best research and knowledge available to us today. The tests are very helpful, but may have “false positive” results. This means we may think that something is wrong with the health of the fetus when, in fact, the fetus is doing well. These tests are still the best guide we have.
- Fetal Kick Counts: This is an old and simple method and involves counting your baby’s movements once or twice a day. It is normal for your baby to have 8 to 10 distinct movements in 2 hours. You can begin doing this at home daily.
- Nonstress Test (NST) combined with Amniotic Fluid Index (AFI): For the NST, a fetal monitor is used to check the heart rate response of your baby. The heart rate of a healthy fetus will increase with fetal movements. The AFI is an ultrasound which measures the amount of amniotic fluid present. This gives us an idea of how well the placenta is working. Both of these tests combined are called a Modified Biophysical Profile and may be done two times per week.
If any of these tests cause concern, a Biophysical Profile may be needed. For this test, the NST is used along with an ultrasound to check fetal breathing movements, other movements, tone, and the amount of fluid present.
What are our choices?
If the results of these tests are normal, you have the choice of waiting until labor starts on its own or having labor induced. Labor can be induced by:
- Prostaglandins: This is a hormone that is applied near the cervix as a gel or timed release insert. Its purpose is to get the cervix ready for labor by helping it soften and thin.
- Pitocin: Medicine is given through an IV to cause the uterus to contract.
- Breaking the bag of waters: This is called amniotomy. If the cervix is ready and the baby’s head is low enough, this may be done to induce labor in women who have had a baby before.
Knowing your options and their risks and benefits can help you decide how to proceed. If you have questions about these choices, please talk with your nurse-midwife or doctor.
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Last Updated: 03/04/2010
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