Still Pregnant after 42 Weeks
Many women believe that if they've passed their expected delivery date (EDD), otherwise referred to as their due date, they have moved into a prolonged pregnancy. However, most of the time they are completely within the normal range of time for a full-term pregnancy and not at all in prolonged pregnancy status.
The term prolonged pregnancy refers to a pregnancy that has exceeded 42 weeks gestation. The counting begins from the start of the last period unless there has been an adjustment according to an ultrasound scan within the first 20 weeks. The phrase "full term" does not mean a specific date on the calendar, but rather it refers to a five week period from 37 weeks to 42 completed weeks of gestation. So, a full-term baby is a baby born any time after 37 weeks and before the end of the 42nd week. More than 80 percent of women deliver within this window of time. When a woman receives her EDD, it is usually a 40 week point which is within the time frame allotted to full term pregnancy.
Babies Come When They're Ready
The fact is that very few babies actually arrive on the date given to the mother by the doctor, even with an ultrasound scan confirming the date. While the numbers vary greatly in studies that have been done on babies that come on the EDD, there is a very small chance of it happening - somewhere between one and six percent. What that tells us is that as long as the pregnancy is low-risk and everything is progressing well, there is no reason to panic if you pass your due date. Between three and ten percent of all pregnancies will arrive at the 42 week mark. After that point, the pregnancy is designated prolonged.
Possible Reasons for Prolonged Pregnancy
There are only a small number of mothers who are affected by prolonged pregnancy. Although the actual cause is not known, some factors are identifiable and could explain, at least in part, why it happens. The reasons may include fetal abnormalities, certain placental enzyme deficiencies and low thyroid hormone levels. However, these compose a very small number of the women who have a prolonged pregnancy. The majority of women who have prolonged pregnancies are those women whose dates were wrong from the start and an ultrasound within the first 20 weeks of gestation was not done.
It is not unusual for an EDD to be overestimated by a month, an error that is usually picked up when the mother goes for her 18 to 20 week ultrasound scan. If this mistake gets by the doctor, then there is no way of knowing or correcting the error late in the pregnancy. Consequently, the supposed 40 week gestation prenatal exam is really only 36 weeks and both mother and doctor will expect the baby to arrive within a two week period. If she doesn't go into labor in that period, she'll be classified as post-term. It is even more common to find errors of one or two weeks.
The reason the error can't be caught after around 20 weeks gestation is that an ultrasound scan, while effective for the first half of pregnancy, loses its effectiveness in the latter half. In the first half of the pregnancy the ultrasound enables certain body measurements to be taken which confirm the age of the baby. Babies grow from that point to different sizes based on assorted factors. So, by the third trimester, the twig is bent and it is futile to try to judge the age of the baby by measurement.
Risk Factors for Prolonged Pregnancy
When a pregnancy moves into prolonged status, it also moves out of low-risk into a high risk situation. Some of the factors that affect this change include:
· a growth rate that is poor
· reduced amniotic fluid in the sac
· vaginal bleeding during pregnancy
· pre-eclampsia and other hypertensive disorders
Some women become fearful for the fate of their babies at the 42nd week mark and ask for intervention. Many times a doctor will do their best to hold off the surgery, avoiding an unnecessary cesarean section. However, if the mother is beside herself with worry, then the doctor will usually act to assuage the fear.
Risks to the Baby
The risk factors to the baby are the same at 42 weeks as they would be for any of the other four weeks in the five week window of full-term pregnancy. However, some doctors like to monitor the baby's situation from this point to ensure all is well. After the 42 week point, the doctor will begin to devise a delivery plan because the risk to the baby begins to increase after 43 weeks.
Very few women are allowed to go beyond 42 weeks without intervention because observational studies have clearly shown that in the 43rd week of pregnancy there is an increased loss of infant life. Some studies say that the rate of fetal loss triples by 43 weeks. The placental function begins to seriously deteriorate, depriving the baby and putting the baby into stress. Labor after a post-term pregnancy is a high risk situation and the baby is monitored very closely.
Learn more about prolonged pregnancy here.