Most pregnancies that involve just one baby last about 40 weeks from the first day of the woman’s last menstrual period. Multiple gestation pregnancies may vary in their duration.

It is usually best to maintain a pregnancy for as long as it is safely possible to allow for continued growth and weight gain as well as fetal brain, liver, and lung development. All of these processes are essential for the health of a newborn.

Infants who are born before 39 weeks are more likely to experience complications, such as breathing difficulties, vision and hearing problems, being unable to stay warm, and feeding difficulties, among other health problems.

However, if a baby is born after 42 weeks, other problems can arise. For this reason, a doctor will sometimes recommend inducing labor.

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A doctor may recommend inducing labor if delivery is late and there are risks to the mother or the baby.

The American College of Obstetricians and Gynecologists (ACOG) recommend classifying full-term pregnancies in one of four ways.

The categories are:

  • Early-term: Delivery occurs between 37 weeks and 38 weeks and 6 days.
  • Full-term: Delivery takes place after 39 weeks but before 40 weeks and 6 days.
  • Later-term: Delivery is within 6 days after 41 weeks.
  • Post-term: Delivery happens at any time after week 42.

Doctors do not know why some women have post-term deliveries, but a 2012 study suggests that possible reasons may include:

  • hormonal factors
  • obesity, possibly because fatty tissue affects the balance of hormones in the body
  • genetic factors, as parents who were born post term appear to be more likely to have a post-term delivery
  • having a baby for the first time

Preventing the risks of a post-term delivery

Post-term pregnancies may carry a higher risk of delivery complications.

Risks to the baby include:

  • increased fetal size, which can make injury more likely during delivery
  • inhaling fecal waste, which can lead to lung problems in the newborn
  • the aging of the placenta and low pH levels in the umbilical cord, leading to neonatal acidemia (low blood pH)
  • issues arising from growth restriction in the womb, such as wrinkled, peeling skin and a thin body due to malnourishment

Risks to the woman include:

  • the need for a cesarean delivery
  • a higher chance of tearing when giving birth
  • an obstructed, slow, or delayed labor
  • a negative emotional effect, as waiting tends to increase anxiety

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If a pregnancy has lasted 42 weeks, a doctor may recommend inducing labor.

In some situations, a doctor may recommend inducing, or bringing on, labor. However, they will first consider the risks, benefits, and necessity of the intervention.

A doctor may recommend inducing labor in instances in which:

  • they have concerns about the health of the woman or baby
  • the post-term date is approaching
  • there is an infection in the uterus
  • there is delayed fetal growth
  • the levels of amniotic fluid are low

Certain medical conditions may pose a risk to the woman or baby, including:

Rh factor is a protein that is sometimes present on the surface of red blood cells. People with this protein in their blood have Rh-positive blood, while those who do not have this protein have Rh-negative blood.

Problems can arise if the fetus has Rh-positive blood, but the woman’s blood is Rh-negative.

Typically, maternal blood does not mix with fetal blood during pregnancy. However, this can sometimes occur during a medical procedure, such as amniocentesis, or if the woman experiences trauma to the abdomen.

If it does happen, the woman will develop antibodies against the Rh factor of the fetus, and her body will fight against the unborn baby’s blood. This attack can be life-threatening for the unborn child, and it can also result in complications with subsequent pregnancies.

If it is necessary to induce labor, a healthcare professional will use certain medications and procedures to cause labor to start.

These procedures include:

Cervical ripening

It is possible to ripen, or dilate, the cervix by inserting a catheter with a small balloon-type device on the end or by introducing a substance that absorbs water.

Amniotomy

A healthcare professional may burst the amniotic sac that surrounds the baby inside the uterus to start labor or to progress labor that has already begun. They can only perform this procedure if the cervix has dilated enough to make the amniotic sac accessible.

Hormones

Doctors may use naturally occurring chemicals called prostaglandins to try to soften and thin out the cervix and encourage cervical dilation. They deliver prostaglandins to the cervix through the vagina. In some cases, they may administer the hormone oxytocin to induce labor by stimulating contractions.

Stripping the membranes

This method can help release prostaglandins to induce labor, according to ACOG. A doctor or midwife will use a finger to “sweep” over the membranes connecting the amniotic sac to the uterine wall.

According to one source, this may be uncomfortable for some women and is only possible following the dilation of the cervix.

As with any medical procedure, labor induction involves some risks.

These include:

  • strong, frequent contractions that can lead to fetal complications, such as an increased heart rate and umbilical cord problems
  • maternal or fetal infections
  • torn uterus
  • increased likelihood of a cesarean delivery
  • fetal death

Some women may seek out natural or nonmedical ways to induce labor at home. However, some of these methods may not be safe.

It is essential to discuss any thoughts of induction with a healthcare professional. There are several factors to consider before deciding on any method of induction. These include the gestational age of the fetus, the fetal position, and any pregnancy complications.

Some natural methods of inducing labor that people have tried include:

Nipple stimulation

Nipple rolling or gentle rubbing may lead to a release of oxytocin, which could help induce labor.

Exercise

Exercise is advisable during pregnancy unless a doctor specifies otherwise. However, there is no evidence that it can induce labor.

Sex

Having sex could help induce labor because orgasms cause uterine contractions, nipple stimulation triggers the release of oxytocin, and semen contains high levels of prostaglandins.

An Iranian study of 120 women concluded that sex during the last week of pregnancy “might be associated with the onset of labor” and could be a natural way to induce this process.

However, a 2012 study of almost 1,200 women in Malaysia found no difference in labor and delivery whether or not the women had sex with the aim of inducing pregnancy.

It is generally safe to have sex during pregnancy, but it is not advisable:

  • after labor has started
  • if the woman has a low-lying placenta
  • if there is vaginal bleeding

In some cases, sex during pregnancy could lead to bleeding, putting the health of both the woman and baby at risk. Women should talk with their doctor if they have any concerns about having sex during pregnancy.

Homeopathy and herbs

Some people recommend herbs and homeopathic remedies to induce labor. The authors of a study that BMJ Open published in 2018 concluded that even though some herbs may be effective, there is a lack of evidence to confirm that they are safe to use.

It is vital to discuss the safety of using herbs to induce labor with a doctor or midwife before trying this method.

Castor oil

Some people have recommended taking castor oil to trigger contractions. Doing this may cause a stomach upset, but it is unlikely to initiate labor.

The authors of a 2012 review concluded that castor oil and evening primrose oil are not likely to induce labor and may increase the risk of complications.

Food

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Some people say that eating pineapple can induce labor, but scientific evidence does not support this.

Anecdotal evidence suggests that some foods, including spicy foods and pineapple, may induce labor.

However, there is a lack of scientific evidence to support these claims, and these foods may worsen acid reflux, which is already a common problem in the later stages of pregnancy.

Some have argued that because pineapple contains an enzyme called bromelain, which people use to tenderize meat, eating it might cause the cervix to soften.

However, stomach acids break down any enzymes in food, so they will not travel directly to the cervix.

In some cases, a doctor may decide that it is necessary to induce labor to try to ensure the safety of the woman and baby.

Several medical procedures can help encourage labor to start, and people can also try a variety of natural methods at home with the approval of their doctor or midwife.

It is important that people speak with their doctor or midwife about any methods of labor induction and the associated risks and benefits.