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Labor

By

Julie S. Moldenhauer

, MD, Children's Hospital of Philadelphia

Reviewed/Revised Mar 2024
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Labor is a series of rhythmic, progressive contractions of the uterus that gradually move the fetus through the lower part of the uterus (cervix) and birth canal (vagina).

Labor occurs in three main stages:

  • First stage: This stage (which has two phases: latent and active) is usually the longest stage. Labor officially begins when there are strong and regular uterine contractions that cause the cervix to open gradually (dilate) and to thin and pull back (efface) until it is fully dilated, and the baby is able to pass into the vagina.

  • Second stage: The mother pushes and the baby is delivered.

  • Third stage: The placenta (an organ that develops inside the uterus to provide oxygen and nutrients to the baby) is delivered. This stage is also called "the afterbirth."

Labor usually starts within 2 weeks of (before or after) the estimated date of delivery. Exactly what causes labor to start is unknown. Toward the end of pregnancy (after 37 weeks), a doctor examines the cervix to try to predict when labor will start.

On average, labor lasts 12 to 18 hours in a woman’s first pregnancy and tends to be shorter, averaging 6 to 8 hours, in subsequent pregnancies. Standing and walking during the first stage of labor can help manage pain and can potentially shorten labor by more than 1 hour.

Stages of Labor

FIRST STAGE

From the beginning of labor to the full opening (dilation) of the cervix—to about 10 centimeters.

Initial (Latent) Phase

  • Contractions are irregular at first but become progressively stronger and more rhythmic.

  • Discomfort is minimal but may increase over time.

  • The cervix begins to thin and dilates to about 4 to 5 centimeters.

  • The initial phase lasts an average of 8 hours (usually no more than 20 hours) in a first pregnancy and 5 hours (usually no more than 14 hours) in subsequent pregnancies.

Stages of Labor

Active Phase

  • The cervix dilates from about 4 centimeters to the full 10 centimeters. It thins and pulls back (effaces) until it merges with the rest of the uterus.

  • The presenting part of the baby (the part of the baby that will deliver first), usually the head, begins to descend into a woman’s pelvis.

  • A woman begins to feel the urge to push as the baby descends, but she should resist it until the cervix is fully dilated. Pushing too early may be unnecessarily tiring and may tear the cervix.

  • This phase averages about 5 to 7 hours in a first pregnancy and 2 to 4 hours in subsequent pregnancies.

Stages of Labor

SECOND STAGE

From the complete opening of the cervix to birth of the baby: This stage usually lasts about 2 hours in a first pregnancy and about 1 hour in subsequent pregnancies. It may last another hour or more if the woman has been given an epidural injection to relieve pain. During this stage, the woman pushes.

Stages of Labor

THIRD STAGE

From birth of the baby to delivery of the placenta: This stage usually lasts only a few minutes but may last up to 30 minutes.

Stages of Labor

Start of labor

Labor usually begins with

  • Contractions in the lower abdomen at regular intervals

  • Sometimes back pain

A woman who has had rapid deliveries in previous pregnancies should notify her doctor as soon as she thinks she is going into labor. When contractions in the lower abdomen first start, they may be weak, irregular, and far apart. They may feel like menstrual cramps. As time passes, uterine contractions become longer, stronger, and closer together. Contractions and back pain may be preceded or accompanied by other signs of labor, such as the following:

If a woman’s membranes rupture, she should contact her doctor or midwife immediately. About 80 to 90% of women whose membranes rupture at or near their due date go into labor spontaneously within 24 hours. If labor has not started after several hours and the baby is due, women are usually admitted to the hospital, where labor is artificially started (induced Induction of Labor Induction of labor is the use of medications to start labor. Usually, when labor needs to be induced, the woman is given oxytocin, a medication that makes the uterus contract more frequently... read more ) to reduce the risk of infection. After the membranes rupture, bacteria from the vagina can enter the uterus more easily and cause an infection in the woman, the fetus, or both.

After a woman with prelabor rupture of membranes is admitted to a birthing center, oxytocin (which causes the uterus to contract) or a similar medication, such as a prostaglandin, is used to induce labor. However, if the membranes rupture more than 6 weeks before the due date (preterm, or before the 34th week), doctors do not typically induce labor until the fetus is more mature.

Admission to a hospital or birthing center

A woman should call her healthcare professional to determine if she should go to a hospital or birthing center when one of the following occurs:

  • The membranes rupture ("water broke").

  • For 1 hour, contractions last at least 30 seconds and occur regularly at intervals of about 6 minutes or less.

At the facility, a healthcare professional will evaluate the mother and fetus. If a pregnant woman is in active labor or membranes have ruptured, the woman is admitted to the labor and delivery unit. If the doctor or midwife is not sure whether labor has started, the woman is usually observed and the fetus is monitored for an hour or so. If labor is not confirmed during that time, she may be sent home.

The Vaginal Exam in Labor
VIDEO

When a woman is admitted to the labor and delivery unit, her vital signs are measured and blood is drawn for analysis.

The presence and rate of fetal heart sounds are recorded, and a physical examination is done. The woman's abdomen is examined to estimate how big the fetus is, whether the fetus is facing rearward or forward (position), and whether the head, face, buttocks, or shoulder is leading the way out (presentation Fetal Presentation, Position, and Lie (Including Breech Presentation) During pregnancy, the fetus can be positioned in many different ways inside the mother's uterus. The fetus may be head up or down or facing the mother's back or front. At first, the fetus can... read more ). Sometimes, an ultrasound is done.

Position and presentation of the fetus affect how the fetus passes through the vagina. The most common and safest combination consists of the following:

  • Head first

  • Facing rearward (facing down when the woman lies on her back)

  • Neck bent forward

  • Chin tucked in

Normal Position and Presentation of the Fetus

Toward the end of pregnancy, the fetus moves into position for birth. Normally, the position of a fetus is facing rearward (toward the woman’s back) with the face and body angled to one side and the neck flexed, and presentation is head first.

Normal Position and Presentation of the Fetus

A vaginal examination using a speculum may be done to determine whether the membranes have ruptured. (A speculum is a metal or plastic instrument that spreads the walls of the vagina apart). The color of the amniotic fluid is noted. The fluid should be clear and have no significant odor. If the membranes rupture and the amniotic fluid is green, the discoloration results from the fetus’s first stool (fetal meconium).

Then the doctor or midwife examines the cervix with their fingers to determine how dilated (noted in centimeters) and how pulled back (effaced) the cervix is (noted as a percentage or in centimeters). This examination may be omitted if the woman is bleeding or if the membranes have ruptured spontaneously.

If there are concerns about complications after the initial examination, fetal monitoring, and laboratory tests, additional testing or monitoring is done.

An intravenous line is usually inserted into the woman’s arm during labor in a hospital. This line is used to give the woman fluids to prevent dehydration and, if needed, to give medications.

When fluids are given intravenously, the woman does not have to eat or drink during labor, although she may choose to drink some fluids and eat some light food early in labor. An empty stomach during delivery makes the woman less likely to vomit. Very rarely, vomit is inhaled, usually after general anesthesia, which can cause severe pneumonia Overview of Pneumonia Pneumonia is an infection of the small air sacs of the lungs (alveoli) and the tissues around them. Pneumonia is one of the most common causes of death worldwide. The most common symptom of... read more Overview of Pneumonia .

Drugs Mentioned In This Article

Generic Name Select Brand Names
Pitocin
NOTE: This is the Consumer Version. DOCTORS: VIEW PROFESSIONAL VERSION
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