When your baby’s due date has passed

It is not possible to predict the date of the birth with certainty. But it's still important to know how far along the pregnancy is and an approximate due date, since that is used to find out whether (and when) inducing labor would be a good idea.

The duration of a pregnancy is always estimated to be 40 weeks from the first day of the last period. Not every women will remember exactly what day that was, though. And some women still have light bleeding at the start of pregnancy, around the time when they would normally have got their period. So they might have been pregnant for a few weeks longer than they realize.

Because there is so much uncertainty about the date of the last period, doctors check to see whether the due date calculated in this way is likely to be correct. They do this by using ultrasound to see how big the baby is. Differences in size between unborn babies are minor in the first few weeks of pregnancy, so it's relatively easy to estimate the age of the embryo and the expected due date. But ultrasound scans aren't entirely accurate either.

It is usually not known why a baby is overdue. Sometimes it is because of a genetic predisposition (hereditary). Women who have already had a baby that came much later than their due date are more likely to have an overdue baby in future pregnancies.

Being born after the 40th week only rarely harms the child. To be on the safe side, though, the doctor or midwife will start doing more checks to see how the woman and her child are doing.

If no abnormalities are found, there isn't any higher risk of complications in the first week after the due date. Even after that, the risk of something happening to the baby doesn't increase much. But certain risks do increase a little. The main risks for the unborn child include:

• The placenta no longer being able to supply the baby with nutrients and oxygen
• An infection developing inside the womb
• Unexpected problems arising during labor

Although being overdue is generally associated with fewer risks for the pregnant woman, childbirth can be more difficult if the child is too big.

Nearly all babies are born by the 3rd or 4th week after the due date. If a baby hasn't been born by then, the risk of being stillborn (dead at birth) increases. Babies are very rarely born that late, though, because labor is usually induced two weeks after the due date at the latest.

If the due date has passed, women typically have two check-ups per week to make sure that she and her baby are doing well. Certain examinations can help to detect potential problems.

These include cardiotocography (CTG, also called a non-stress test) and ultrasound scans. The CTG is used to monitor the baby’s heart rate. The ultrasound scan is used to check the baby’s size and the amount of amniotic fluid around the baby. You might also be checked for signs of infection, especially if amniotic fluid has been leaking. Other tests are sometimes used to determine what is known as the baby’s “biophysical profile.” For example, one of these tests involves counting his or her movements.

At the end of the day, the decision of whether to induce labor – and, if so, when to induce it – is a personal decision made by the parents-to-be. They can first find out all about the advantages and disadvantages of inducing labor and then make the decision together with the medical team involved in the process.

Doctors usually suggest inducing labor if there are signs of possible complications that mean the baby needs to be born soon – but the problem isn’t serious enough for the baby to be delivered by Cesarean.

Even if there aren't any signs of complications, doctors usually recommend inducing labor starting one week after the due date. The due date is often confirmed again beforehand using ultrasound.

If the baby still hasn’t been born more than one week after the due date, inducing labor can lower the risk of the child dying. Research has found the following:

• Without induced labor: When labor wasn’t induced after a certain amount of time, about 3 out of 1,000 overdue babies died.
• With induced labor: When labor was induced after 41 completed weeks of pregnancy, about 1 out of 1,000 overdue babies died.

Inducing labor can also lower the risk of needing a Cesarean section.

There are many traditional methods that women use to try to get labor started, including things like going on long walks. Some women try to induce labor by having sex or stimulating their nipples. These approaches are based on the theories that hormones in men’s semen (the sperm-carrying fluid that is released during ejaculation), and hormones that women’s bodies make when sexually aroused, cause the pregnant woman’s cervix to relax and open more easily.

There has even been research on these approaches. But it only produced weak evidence suggesting that stimulating nipples for about one to three hours per day might help. It is not clear whether having sex can help the birth start sooner.

Some women drink raspberry leaf tea to soften the cervix, while others use homoeopathy, evening primrose oil, acupuncture, or hypnosis. But there is no scientific proof that these approaches work.

Castor oil is also traditionally used to induce labor. It is available in the form of a juice, a solution used in colonic irrigation, or capsules that are swallowed. This oil has not been proven to have a positive effect. But research has shown that it causes nausea in most women. There is not enough research on the safety and effectiveness of castor oil.

There are several different methods that doctors commonly use to induce labor.

• Hormones to "ripen" the cervix: The cervix is the opening or “neck” of the womb. It is tightly closed throughout the pregnancy. When the body starts preparing for birth, hormones make the cervix relax and become softer. A cervix that is ready for labor is sometimes called a “ripe” cervix. Hormones, especially hormones called prostaglandins, may be applied to the cervix in the form of a gel to prepare it for birth. This approach is the most commonly used one.
• Balloon catheters: Balloon catheters are sometimes used to stretch and open the cervix as well. These are small tubes that are inserted into the vagina and womb, and then filled with liquid.

Sometimes these measures are enough to set the birth off. If they don't work, there are still other steps that can be taken:

• Hormones to start contractions: These are typically either prostaglandins or oxytocin. They can be swallowed, inserted into the vagina in the form of tablets or suppositories, or “fed” into a vein in your arm using an infusion (an IV drip).
• Opening the amniotic sac: When labor contractions start, the amniotic sac can also be opened (“the water broken”) to help things along. The amniotic sac is the fluid-filled bag that the baby is inside. This can be done my making a small incision (cut) called an amniotomy. Once a woman’s water breaks, the amniotic sac can't be closed again. So it's important that labor starts quite soon afterwards, because the baby is no longer protected by the amniotic fluid.
• Membrane sweep: Sometimes labor can also be induced with the help of a “membrane sweep.” This is where the membranes of the sac surrounding the baby are gently separated from the wall of the womb using a finger.

Neither of these two approaches are typically painful, but most women find them to be unpleasant.

Labor induced with hormones doesn't cause any serious problems in most women. But there are possible side effects. The main side effects of prostaglandins are gastrointestinal problems like nausea, vomiting and diarrhea. Oxytocin can cause water retention and other problems involving fluid balance, such as low sodium levels.

The amount of hormones given is adjusted to make induced contractions as normal as possible – in other words, not too frequent and not too strong. Induced labor should not force a birth, but help it happen as naturally as possible. This doesn't always work because it's hard to predict what sort of effect the selected dose will have on the course of the birth.

When labor is induced, more tests are needed than usual. Although these might be unpleasant, most women don't find this or other aspects of labor induction particularly distressing. The relief of finally being able to give birth to their child often overrides other feelings.

Women generally have very different experiences of induced labor: While some would do it again, others would rather avoid it if they give birth again.

Inducing labor doesn't necessarily mean that everything will happen really quickly either: Many women are surprised how long it still takes for their baby to arrive.

It can be helpful to ask your midwife or doctor about the options for inducing labor in your hospital, and about the associated advantages and disadvantages. Induction of labor isn't an emergency – there is usually enough time to get used to the idea and have all your questions answered.