Topic Resources
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) to the outside world.
(See also Overview of Labor and Delivery.)
Labor occurs in three main stages:
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First stage: This stage (which has two phases: initial and active) is labor proper. Contractions cause the cervix to open gradually (dilate) and to thin and pull back (efface) until it merges with the rest of the uterus. These changes enable the fetus to pass into the vagina.
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Second stage: The baby is delivered.
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Third stage: The placenta is delivered.
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 36 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
shorten it by more than 1 hour.
Stages of Labor
FIRST STAGE
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From the beginning of labor to the full opening (dilation) of the cervix—to about 4 inches (10 centimeters).
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Initial (Latent) Phase
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Active Phase
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SECOND STAGE
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From the complete opening of the cervix to delivery 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 or a drug to relieve pain.
During this stage, the woman pushes.
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THIRD STAGE |
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From delivery of the baby to delivery of the placenta: This stage usually lasts only a few minutes but may last up to 30 minutes.
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Start of labor
All pregnant women should know what the main signs of the start of labor are:
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Contractions in the lower abdomen at regular intervals
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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, abdominal contractions become longer, stronger, and closer
together. Contractions and back pain may be preceded or accompanied by
other clues, such as the following:
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Bloody show: A small discharge of blood mixed with mucus from the vagina is usually a clue that labor is about to start. The bloody show may appear as early as 72 hours before contractions start.
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Rupture of membranes: Usually, the fluid-filled membranes that contain the fetus (amniotic sac) rupture when labor begins, and the amniotic fluid flows out through the vagina. This event is commonly described as “the water breaks.” Occasionally, the membranes rupture before labor starts. Rupture of membranes before labor begins is called premature rupture of membranes. Some women feel a gush of fluid from the vagina, followed by steady leaking.
If a woman’s membranes rupture before labor starts, 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)
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.
Oxytocin (which causes
the uterus to contract) or a similar drug, such as a prostaglandin, is
used to induce labor. However, if the membranes rupture more than 6
weeks before the due date (prematurely, 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 go to a hospital or birthing center when one of the following occurs:
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The membranes rupture.
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Strong contractions occur 6 minutes apart or less and last 30 seconds or more.
If rupture of membranes is suspected or the cervix is dilated
more than 1 1/2 inches (4 centimeters), the woman is admitted. If the
doctor or midwife is not sure whether labor has started, the woman is
usually observed and the fetus is monitored for a hour or so, and if
labor is not confirmed by then, she may be sent home.
When the woman is admitted, the strength, duration, and frequency
of contractions are noted. The woman's weight, blood pressure, heart
and breathing rates, and temperature are measured, and samples of urine
and blood are taken for analysis. Her 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).
Position and presentation of the fetus affect how the fetus passes through the vagina. The most common and safest combination consists of the following:
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Head first
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Facing rearward (facing down when the woman lies on her back)
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Face and body angled toward the right or left
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Neck bent forward
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Chin tucked in
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Arms folded across the chest
Head first is called a vertex or cephalic presentation. During
the last week or two before delivery, most fetuses turn so that the back
of the head presents first. An abnormal position or presentation—such
as buttocks first (breech) or shoulder first or the fetus is facing
forward—makes delivery considerably more difficult for the woman, fetus,
and doctor. Cesarean delivery is recommended.
Normal Position and Presentation of the Fetus
Toward the end of pregnancy, the fetus moves into position for
delivery. 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.
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A vaginal examination is done to determine whether the membranes have ruptured and how dilated (noted in centimeters) and effaced the cervix is (noted as a percentage or in centimeters), but this examination may be omitted if the woman is bleeding or if the membranes have ruptured spontaneously. 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).
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 drugs.
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. Inhaling vomit can cause inflammation
of the lungs, which can be life threatening. Antacids are typically
given to women who are having a cesarean delivery to reduce the risk of
damage to the lungs if vomit is inhaled.
Fetal monitoring
Soon after the woman is admitted to the hospital, the doctor or
another health care practitioner listens to the fetus’s heartbeat
periodically using a type of stethoscope (fetoscope) or a handheld
Doppler ultrasound device or continuously using electronic fetal heart
monitoring. Practitioners monitor the fetus's heart to determine whether
the fetus's heart rate is normal and thus whether the fetus is in distress.
Certain abnormal changes in the fetus’s heart rate during contractions
can indicate that the fetus is not receiving enough oxygen.
The fetus’s heart rate can be monitored in the following ways:
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Externally: An ultrasound device (which transmits and receives ultrasound waves) is attached to the woman’s abdomen. Or a fetoscope is placed on the woman's abdomen at regular intervals.
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Internally: An electrode (a small round sensor attached to a wire) is inserted through the woman’s vagina and attached to the fetus’s scalp. The internal approach is typically used when problems during labor appear likely or when signals detected by the external device cannot be recorded. This approach can be used only after the membranes that contain the fetus have ruptured (described as "the water breaks").
Use of an external ultrasound device or internal electrode to
monitor the fetus's heart rate is called electronic fetal monitoring.
Electronic monitoring is used to continuously monitor the contractions
of the uterus. It is used for virtually all high-risk pregnancies and,
in many practices, for all pregnancies.
In a high-risk pregnancy,
electronic monitoring is sometimes used as part of a nonstress test, in
which the fetus’s heart rate is monitored as the fetus lies still and
as it moves. If the heart rate does not speed up as expected on two
occasions within 20 minutes of when the fetus moves, the heart rate is
described as nonreactive or nonreassuring. Then an ultrasound
biophysical profile may be done to check on the fetus's well-being.
For an ultrasound biophysical profile, ultrasonography is
used to produce images of the fetus in real time, and the fetus is
observed. After 30 minutes, doctors assign a score of 0 or 2 to the
following:
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Results of the nonstress test (reactive or nonreactive)
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Amount of amniotic fluid
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Presence or absence of a period of rhythmic breathing
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Presence or absence of at least three clearly visible movements of the fetus
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Muscle tone of the fetus, indicated by stretching, then flexing the fingers, a limb, or the trunk
A score of up to 10 is possible.
Based on the result, doctors may allow labor to continue or may do a cesarean delivery immediately.
During the first stage of labor, the heart rate of the
fetus is monitored periodically with a stethoscope or an ultrasound
device or continuously using electronic monitoring. Monitoring the
fetus’s heart rate is the easiest way to determine whether the fetus is
receiving enough oxygen. Abnormalities in the heart rate (too fast or
too slow) and variations in the heart rate (over time and in response to
contractions) may indicate that the fetus is in distress (fetal distress). The heart rate of the woman is also monitored periodically.
During the second stage of labor, the fetus’s heart rate
is monitored after every contraction or, if electronic monitoring is
used, continuously. The woman’s heart rate and blood pressure are
monitored regularly.
Pain relief
With the advice of her doctor or midwife, a woman usually plans
an approach to pain relief long before labor starts. She may choose one
of the following:
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Natural childbirth, which relies on relaxation and breathing techniques to deal with pain
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Analgesics (given intravenously)
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A particular type of anesthetic (local or regional) if needed
After labor starts, these plans may be modified, depending on how
labor progresses, how the woman feels, and what the doctor or midwife
recommends.
A woman’s need for pain relief during labor varies considerably,
depending to some extent on her level of anxiety. Attending childbirth
preparation classes helps prepare the woman for labor and delivery. Such
preparation and emotional support from the people attending the labor
tend to lessen anxiety.
Analgesics (pain relievers) may be used. If a woman
requests analgesics during labor, they are usually given to her.
However, because some of these drugs can slow (depress) breathing and
other functions of the newborn, the amount given is as small as
possible. Most commonly, an opioid such as fentanyl or morphine
is given intravenously to relieve pain. These drugs may slow the
initial phase of the first stage of labor, so they are usually given
during the active phase of the first stage. In addition, because these
drugs have the greatest effect during the first 30 minutes after they
are given, the drugs are often not given when delivery is imminent. If
they are given too close to delivery, the newborn may be overly sedated,
making adjustment to life outside the uterus more difficult. To
counteract the sedating effects of these drugs on the newborn, a doctor
can give the newborn the opioid antidote naloxone immediately after delivery.
Local anesthesia numbs the vagina and the tissues around
its opening. This area can be numbed by injecting a local anesthetic
through the wall of the vagina into the area around the nerve that
supplies sensation to the lower genital area (pudendal nerve). This
procedure, called a pudendal block, is used only late in the second
stage of labor, when the baby’s head is about to emerge from the vagina.
It has been largely replaced by epidural injections. A more common but
less effective procedure involves injecting a local anesthetic at the
opening of the vagina. With both procedures, the woman can remain awake
and push, and the fetus’s functions are unaffected. These procedures are
useful for deliveries that have no complications.
Regional anesthesia numbs a larger area. It may be used for women who want more complete pain relief. The following procedures can be used:
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Lumbar epidural injection is almost always used when pain relief is needed. An anesthetic is injected in the lower back—into the space between the spine and the outer layer of tissue covering the spinal cord (epidural space). Alternatively, a catheter is placed in the epidural space, and a local anesthetic (such as bupivacaine) is continuously and slowly given through the catheter. An opioid (such as fentanyl or sufentanil) is often also injected. An epidural injection for labor and delivery does not prevent the woman from pushing and does not make women more likely to need a cesarean delivery. An epidural injection can also be used in cesarean deliveries.
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Spinal injection involves injecting an anesthetic into the space between the middle and inner layers of tissue covering the spinal cord (subarachnoid space). A spinal injection is typically used for cesarean delivery when there are no complications.
Occasionally, use of either an epidural or a spinal injection
causes a fall in blood pressure. Consequently, if one of these
procedures is used, the woman’s blood pressure is measured frequently.
Epidural
VIDEO
General anesthesia makes a woman temporarily unconscious.
It is rarely necessary and infrequently used because it may slow the
function of the fetus’s heart, lungs, and brain. Although this effect is
usually temporary, it can interfere with the newborn’s adjustment to
life outside the uterus. General anesthesia is typically used for
emergency cesarean delivery because it is the quickest way to
anesthetize the woman.
Natural childbirth
Natural childbirth uses relaxation and breathing techniques to control pain during childbirth.
To prepare for natural childbirth, a pregnant woman and her
partner take childbirth classes, usually six to eight sessions over
several weeks, to learn how to use the relaxation and breathing
techniques. They also learn what happens in the various stages of labor
and delivery.
The relaxation technique involves consciously tensing a part of
the body and then relaxing it. This technique helps a woman relax the
rest of her body while the uterus is contracting during labor and relax
her whole body between contractions.
The breathing technique involves several types of breathing,
which are used at different times during labor. During the first stage
of labor, before the woman begins to push, the following types of
breathing may help:
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Deep breathing with slow exhalation to help the woman relax at the beginning and end of a contraction
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Fast, shallow breathing (panting) in the upper chest at the peak of a contraction
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A pattern of panting and blowing to help the woman refrain from pushing when she has an urge to push before the cervix is completely open (dilated) and pulled back (effaced)
The woman and her partner should practice relaxation and
breathing techniques regularly during pregnancy. During labor, the
woman’s partner can help her by reminding her of what she should be
doing at a particular stage and by noticing when she is tense, in
addition to providing emotional support. The partner may massage the
woman to help her relax more.
The most well-known method of natural childbirth is probably the
Lamaze method. Another method, the Leboyer method, includes birth in a
darkened room and immersion of the baby into lukewarm water immediately
after delivery.
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