The right moment for birth is different for every pregnancy and baby. Even though pregnancy is commonly said to last nine months, the reality can be different. Doctors measure pregnancy in weeks from the first date of your last menstrual period.
After 42 weeks, the risk of stillbirth increases from 2–3 in 1000 births to 4–7 in 1000 births.
Other risks to the baby include increased size, malnourishment, umbilical cord compression, and having a bowel movement inside the womb.
Risks to the mother include the increased potential for a long labor, birth injuries, infections, and c-section.
Close monitoring of your baby’s health is essential if you are past your due date.
The decision to start labor happens between you and your doctor. It depends on your baby’s health, your wishes, and your body’s readiness.
Full term, when the baby reaches full development and is ready to be born, happens in the range of 38–42 weeks. Once you get beyond 42 weeks pregnant, the risk increases for the baby and mother.
Why haven't I gone into labor?
There are several reasons why a pregnancy may go to 42 weeks. The most common cause is an inaccurate due date. It is called the estimated due date for a reason. It is just an estimate!
An ultrasound in the first trimester is the most accurate estimate of your due date. You can also count 40 weeks from the first day of your last menstrual period (LMP) to find the due date. If you are unsure when your last period was or if you have irregular periods, this method can give you a due date that is inaccurate by weeks.
Some women do not ovulate — release the egg that gets fertilized and begins pregnancy — at precisely the same point each menstrual cycle. In fact, in one study, doctors had to revise the due dates after ultrasound in 40% of women.
Some pregnancies genuinely go beyond 42 weeks. The reason for this is not certain, but it could be due to genetics or the size and position of the baby.
Risks of going past 42 weeks pregnant
In post-term pregnancies, there are increased risks to both the mother and baby. As time passes, the placenta — the temporary organ that supplies the baby with nutrients and oxygen — ages and can develop small deposits of calcium and minerals that block blood vessels. Other risks include:
- Stillbirth. After 42 weeks, the risk of stillbirth (infant death) increases. At the end of pregnancy and before 42 weeks, the risk is about 2 to 3 deaths per 1000 births in developed countries. After 42 weeks, this increases to 4 to 7 deaths per 1000 births.
- Increased size. Usually, babies continue to grow after their due date. This increased size can make labor and delivery longer and more difficult and can necessitate a c-section.
- Malnourishment. Some babies stop gaining weight after the due date due to problems with the blood flow through the placenta. This lack of growth is because of malnourishment.
- Decreased amniotic fluid. As time passes, the amount of fluid surrounding the baby (amniotic fluid) decreases. With less cushioning fluid around it, the umbilical cord may become pinched.
- Bowel movement in the womb. Babies who stay in the womb longer are more likely to have a bowel movement while they are inside. This situation can be dangerous during delivery if the baby breathes in the amniotic fluid.
- Maternal risks. Mothers who have babies after 42 weeks are likelier to have long labors, injuries, tearing of the external genitals during delivery, and c-sections. They are also more likely to get infections.
Do I need a labor induction?
The decision to induce labor is different for each person and happens between you and your healthcare team. Your provider will closely monitor you and your baby if you have not gone into labor after your due date. Many factors must be considered, including:
- The baby's size and growth. Your healthcare team can monitor this with ultrasound.
- The baby's oxygen supply. A non-stress test tracks patterns of the baby’s heartbeat to show this.
- The baby’s movements and the amount of amniotic fluid. These can also be measured by ultrasound.
- Maternal age and health status. If you are older than 35, a teenager, a smoker, have health problems, or have complications in your pregnancy, your doctor may want to induce labor sooner.
- Your desires. Your healthcare team should work to respect your wishes while protecting the health of you and your baby.
For most pregnancies, doctors recommend inducing labor when you reach 41 weeks. There is an increase in risk to the baby inside the womb between 41 and 42 weeks and more significant risks after 42 weeks.
What to expect with labor induction
There are a variety of ways to induce labor:
- Intravenous medication. Your healthcare team can give you medicine through an intravenous line. This medicine is called Pitocin. It is a synthetic version of the hormone that naturally causes labor contractions.
- Vaginal suppository. Medicine in tablet (suppository) form can be placed inside the vagina to make the cervix softer. It may cause contractions or may help your body prepare for labor.
- Balloon catheter. A doctor can insert a small catheter (tube) with a balloon inside it into the opening of the cervix. This balloon is filled with sterile water after the catheter is in place and causes the cervix to open.
Water breakage. If there is some dilation and the baby’s head is low in the birth canal, your provider may be able to break your water. When your water breaks, it helps labor start by increasing the pressure of the baby’s head on the cervix.
Your provider may use a combination of these methods. If you would like, you may be able to get an epidural to help with pain during your induction.
Induced labor can take a long time or a short time. It all depends on your body’s response to the method your doctor uses and other factors, such as the size and position of the baby. Frequently changing your position as labor progresses can help.
Do I need a c-section?
If you have had a c-section before, your doctor may recommend one. A c-section is considered major surgery and brings many risks, including bleeding, infection, and blood clots. If your baby is healthy and has enough oxygen, your doctor should try labor induction first.
Even though there are some risks to pregnancy beyond the due date, most babies born after term are born healthy. The risks increase as you approach 42 weeks, so it is important to work with your healthcare team to monitor your baby closely.
- Institute for Quality and Efficiency in Healthcare. Pregnancy and birth: When your baby’s due date has passed.
- UpToDate. Patient education: Postterm pregnancy (Beyond the Basics).
- American Academy of Family Physicians. Pregnancy: What to expect when you’re past your due date.
- Americal Journal of Obstetrics and Gynecology. Mortality risk of expectant management compared with delivery stratified by gestational age and rate and ethnicity.
- American College of Gynecologists. Management of Stillbirth.
- American College of Gynecologists. Methods for estimating the due date.