What is labor?

Labor is the process by which contractions of a pregnant uterus cause birth. During labor the cervix thins (effacement) and opens (dilatation). The baby moves down the birth canal and is born. Delivery of the placenta is the last part of labor.

Every labor is different. How long it lasts and how it progresses differ from woman to woman and from birth to birth. There are, however, general guidelines for labor that a health care provider uses to decide whether it is progressing normally. If it is not progressing normally, you may need medical assistance or a cesarean section.

If any signs of labor occur before 37 weeks of pregnancy, the labor is considered preterm. You should call your health care provider right away if you have any signs or symptoms of labor before 37 weeks.

How does labor start?

No one knows exactly what starts the labor process. However, we do know that certain hormones, such as oxytocin and prostaglandin, cause uterine contractions and the thinning of the cervix. Perhaps hormones from the baby trigger labor by stimulating the mother's hormone production.

Sometimes knowing when labor has begun is difficult. You may be admitted to the hospital and then sent home if your labor does not progress--that is, if your cervix does not efface (thin out) or dilate. (This is called false labor).

What happens during labor?

The beginning of labor is defined as the beginning of opening and thinning of the cervix caused by regular uterine contractions. There are some general signs that a woman's body is preparing for labor:

• Passage of a small amount of blood-tinged mucus from the vagina, called "show" or the mucus plug. This may occur 1 day to several weeks before labor begins or after a vaginal exam.
• Breaking of the bag of waters (the amniotic sac). If this happens, contact your health care provider right away and go to the hospital.

While the two signs above are clear warning signs that labor is about to begin, there is only one real sign that labor has very likely started:

• regular, strong contractions that last more than 30 seconds.

There are three stages of labor. By the end of the first stage, the cervix has dilated fully to 10 centimeters (cm). The first stage of labor is divided into early and active phases and usually lasts several hours.

• Early labor, or prelabor, is when your cervix is 0 to 3 cm dilated.
• Active labor begins when the cervix is 3 to 4 cm dilated. The contractions usually become stronger and more frequent, and the cervix dilates faster. The average woman in her first labor may dilate about 1 cm per hour during the active phase of labor. If you have had a baby before, you usually progress faster.

The baby is born during the second stage of labor. This is when you push the baby down the birth canal. This stage of labor usually lasts 15 to 75 minutes but may last as long as 2 or 3 hours, depending on several factors. These factors include previous births, the position of the baby's head, and the size of the baby and the birth canal.

During the third stage of labor you deliver the placenta. This usually happens within 30 minutes after the birth of the baby.

The first few hours after delivery are called postpartum recovery. During this time, the uterus continues to contract as it becomes firm and smaller. A small amount of bleeding continues and becomes less and less. Your pulse and blood pressure return to normal.

How are problems in labor identified?

Ensuring that your labor is normal requires skill, experience, and careful monitoring by your health care provider. Your vital signs, your uterine contractions, and your baby's heart rate must be checked throughout labor. These checks can be done manually or with an electronic monitor. They help your health care provider detect problems and take appropriate action.

During prenatal visits you and your partner should discuss with the health care provider any questions you have about labor. You should also discuss procedures, such as electronic monitoring and cesarean section, that may become necessary during labor and delivery.