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McKesson Clinical Reference Systems: Women's Health Advisor 2002.2
Postdate Pregnancy
In this discussion you will learn what postdate pregnancy
is, what tests are used to diagnose it, and how it is
treated. Because there are some very serious risks for both
the mother and the baby, the doctor will follow a postdate
pregnancy closely.
What is postdate pregnancy?
The length of a normal pregnancy is 40 weeks from the first
day of the last menstrual period. A postdate pregnancy is a
pregnancy that lasts longer than 42 weeks.
How does it occur?
Three percent to 12% of all pregnancies are postdate.
Sometimes this is because the due date is incorrect. In
other cases pregnancies last longer than 40 weeks. Why some
pregnancies continue past their due dates is not well
understood.
How is it diagnosed?
You and your doctor must first accurately date your
pregnancy. It is much easier to calculate an accurate due
date early in the pregnancy. This is one reason you need
prenatal care early in your pregnancy.
The doctor uses several kinds of information to calculate
your due date, including the date of your last menstrual
period and how regular your periods are. An ultrasound
scan may be used to measure the baby and estimate the due
date. This estimate is usually accurate within 7 to 10 days
if the ultrasound scan is done during the first half of the
pregnancy.
How is it treated?
If you go past your due date, the concern is that the
placenta is aging. It may no longer be providing enough
oxygen and nutrients to your baby.
There are several ways to check the health of an overdue
baby:
- a kick count, where you count movements your baby makes
during a prescribed length of time
- electronic fetal monitoring (nonstress test)
- ultrasound evaluation (biophysical profile)
- ultrasound measurement of the amount of amniotic fluid.
If the health of your baby is unclear or dates are
uncertain, your doctor may do an amniocentesis. For this
test some amniotic fluid is taken from your uterus. Tests
of the fluid can show how mature your baby's lungs are.
Your doctor will check for meconium in the amniotic fluid.
Meconium is a greenish substance that builds up in your
baby's bowels and is normally discharged shortly after
birth. If it is discharged into the amniotic fluid before
birth, the baby might inhale it. Inhalation of meconium
into the lungs can cause severe breathing problems for the
baby at birth. If meconium is found, your baby will be
monitored very closely.
All of this information helps your doctor determine whether
it is safe to wait for labor or if it is time to induce
labor to deliver the baby.
- At 42 weeks your doctor may induce labor, especially if
your cervix has ripened and is ready for delivery.
(Inducing labor means starting it artificially, such as
with medication.)
- If the baby appears to be healthy and not in danger, your
doctor may check you regularly and wait for labor to
begin naturally.
- If the baby appears to be in danger, labor may have to be
induced, or the baby may be delivered by cesarean
section.
What are the risks?
- If the pregnancy continues, your baby may not receive
enough oxygen or nutrients from the blood of an aging
placenta. This could stop the baby's growth, damage the
baby's brain, or even kill the baby.
- Discharge and inhalation of meconium by the baby could
cause severe breathing difficulties after birth.
What can be done to prevent stillbirth or harm to my baby?
The most important thing you can do to have a healthy baby
is to see a doctor and begin prenatal care as soon as you
think you are pregnant.
If you have passed your due date, your doctor may avoid
possible harm to your baby by inducing labor as your
pregnancy nears 42 weeks. However, there are risks if the
baby is not mature and ready to be born. Also, if your
cervix is not yet ready for labor, you could have problems
such as prolonged labor and infection. Delivery by
cesarean section might become necessary. Make sure that you
discuss all risks and options with your doctor before
delivery.
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