What is the concern about pregnancy that lasts longer than 42 weeks?
The average length of a normal term pregnancy is 37 to 42 weeks from the first day of the last menstrual period. The due date is considered to be at 40 weeks. When a pregnancy lasts longer than 40 weeks, it is called a postterm pregnancy. If you go past your due date, the concern is that the placenta has gotten older and may not work as well as it needs to. It may no longer be able to bring enough oxygen and nutrients to the baby. This can make it more likely that there will be complications for both you and the baby.
If you do not deliver by your due date, your healthcare provider may watch your pregnancy more closely. The chances of a problem for the baby slowly start to increase after around 41 weeks. The risks for both mother and baby get much higher after 42 weeks. If you are still pregnant after 42 weeks, your healthcare provider will follow your pregnancy very closely or recommend delivery.
What is the cause?
Sometimes pregnancies go past the due date because the due date is wrong. But it is not well understood why some pregnancies last longer than 40 weeks.
How is it diagnosed?
You and your healthcare provider must first accurately date your pregnancy. It is much easier to calculate an accurate due date early in the pregnancy. This is one of the reasons for starting prenatal care early.
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 ultrasound scan may be done to measure the baby and estimate the due date. This estimate is usually more accurate if the scan is done during the first half of the pregnancy.
There are several ways to check on your health and the baby’s health and determine what treatment may be needed.
Ways to check the health of the baby include:
- Checking the baby’s movements by doing a kick count. This means that you count movements your baby makes during a certain length of time.
- Electronic fetal heart rate monitoring (nonstress or contraction stress test)
- An ultrasound test called a biophysical profile
- Measurement of the amniotic fluid with ultrasound
How is it treated?
Information from these 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 tests show that there may be a problem, labor may have to be induced, or the baby may be delivered by C section.
- After 41 to 42 weeks your provider may induce labor, especially if your cervix has ripened and is ready for delivery.
What are the risks of pregnancy after 42 weeks?
Examples of risks to the baby include:
- If the pregnancy continues, your baby may not get enough oxygen or nutrients from the placenta. This could stop the baby's growth or harm the baby's brain. It might even cause death of the baby.
- The baby may make its first bowel movement inside the uterus. The bowel movement is called meconium. Most of the time meconium is first passed by the baby after it is born. If it happens in the amniotic fluid before birth, the baby may breathe the meconium into the lungs. This could cause serious breathing problems after birth, although most of the time, meconium does not cause any major problems.
- You may develop a problem called oligohydramnios, which means too little amniotic fluid around the baby. This may make if harder for the baby to tolerate the stress of labor.
- The baby may have low blood sugar.
- Babies delivered postterm are more likely to need care in an intensive care unit.
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 the baby is delivered too early and is not ready to be born. Also, if your cervix is not ready for labor, you could have problems, such as prolonged labor and infection. In this case, you might need to have a C-section.
Make sure that you discuss the risks and options of delivery with your healthcare provider.
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