You’ve probably heard that the length of pregnancy is 40 weeks from your last menstrual period.
Babies are currently considered full-term when they are delivered between weeks 39 and 41. They are considered late-term between weeks 41 and 42. Babies delivered after this window of time are considered post-term, or post-date.
Here’s more about what you can expect if your pregnancy stretches beyond your original due date and into post-date territory.
How are due dates calculated?
Doctors typically calculate your due date using the date of your last menstrual period (LMP). You aren’t actually carrying your baby in those first two weeks, but they still count as the start of your pregnancy.
For women with irregular cycles, or for those who weren’t tracking their cycles, this practice can be unreliable at best. Thankfully, there are other ways to determine when your baby might arrive.
Your doctor will usually confirm the dating of your pregnancy using an ultrasound. This will be performed sometime during the first trimester. At this appointment, the ultrasonographer will measure the embryo or fetus to find its crown-to-rump length and corresponding gestational age.
Measurements in early pregnancy are very reliable when determining gestation. This date may be used instead of the LMP date if there’s a large discrepancy between the two.
In 2013, the American College of Obstetricians and Gynecologists (ACOG) changed the definitions for the stages in the final weeks of pregnancy. The changes reflect research about different gestations and their abilities to survive and thrive outside the womb.
The new definitions are as follows:
- 37 to 39 weeks is early-term
- 39 to 41 weeks is full-term
- 41 to 42 weeks is late-term
- 42 weeks (or more) is post-term
About 7 percent of pregnancies end up going post-term. The good news is that early ultrasound has decreased the incidence of post-term pregnancies by giving doctors better tools for estimating true fetal age.
Still, some accurately dated pregnancies may go beyond 42 weeks.
You might be at risk of a post-term pregnancy is you have had a post-date pregnancy in the past. The same goes if being overdue runs in your family.
You may want to discuss your personal or family history with your doctor at your first prenatal appointment. They might want to put together a plan if you deliver after your due date.
Other risk factors include:
- not knowing the exact date of your LMP
- being a first-time mom
- carrying a boy
Occasionally, you may not go into labor on time if there’s an issue with the placenta or baby. But this situation is rare.
The placenta may not work as well as your pregnancy continues.
Along with a higher chance of having a cesarean delivery, your baby is also at risk of developing:
- dysmaturity syndrome
- meconium aspiration
Stillbirth is another serious complication of a post-term delivery.
When you pass your due date, your doctor will likely want to see you frequently to assess your health. Your doctor will also regularly check the health of your baby to make sure everything is OK.
There are a number of tests you might encounter at this stage.
- Nonstress test. This test is like kick counting. You will press a button any time you feel your baby move. Your responses will be recorded onto a piece of paper that also shows the fetal heart rate.
- Biophysical profile. This comprehensive test combines electronic fetal monitoring with ultrasound technology. Your baby’s heart rate, amniotic fluid, breathing, movement, and muscle tone are all assessed.
- Contraction stress test. Your doctor will induce contractions for this test. Then your baby’s cardiac activity is measured in response to the contractions.
At home, it’s also a good idea to count kicks. CountTheKicks.org suggests getting into a comfortable position on your side. Count each movement as a kick until you reach 10 total.
You should be able to feel 10 kicks in a half hour to two-hour period. If not, drink fluids or gently touch your baby to wake him up. Try to count kicks at the same time each day for the most consistent results.
Though you’re running out of space in your uterus, your baby’s activity is a good indication of their health. If you notice that things are especially quiet one day, it might be a good idea to call or visit your doctor.
Your doctor may discuss inducing labor when you are one to two weeks past your due date. Labor induction is all about preparing the cervix to open and facilitate a vaginal delivery.
There are several methods of induction, including the following.
- Ripening the cervix. Your doctor may use a device or prostaglandins to encourage your cervix to soften.
- Sweeping membranes. Your doctor will insert a finger and sweep between the amniotic sac and wall of your uterus. Some women go into labor within 48 hours of having this procedure.
- Rupturing membranes. Your doctor will make a small hole into your amniotic sac to break your waters. Most women go into labor within hours of having this procedure.
- Drugs. Your doctor will administer IV medication (oxytocin) that will cause your uterus to contract.
If these methods don’t send you into labor, you doctor will likely discuss a cesarean delivery. A cesarean is a surgical procedure where the baby is delivered through an incision in your abdomen and uterus.
In most cases, you will be awake for this procedure. But you’ll be given pain medication through an epidural or spinal block.
Carrying your pregnancy well beyond your due date can be terribly uncomfortable and disheartening. But rest assured that your doctor will keep a good eye on you. They will suggest a course of treatment to keep both you and baby safe.
Though it may feel like it, you won’t be pregnant forever. As the days and weeks roll on, discuss any and all concerns with your doctor.