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.
Labor occurs in three main stages:
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 through the vagina.
Second stage: The baby is delivered.
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.
Initial (Latent) Phase
Contractions become progressively stronger and more rhythmic.
Discomfort is minimal.
The cervix thins and opens to about 1½ inches (4 centimeters).
This phase lasts an average of 8½ hours (up to 20 hours) in a first pregnancy and 5 hours (up to 12 hours) in subsequent pregnancies.
Active Phase
The cervix opens from about 1½ inches (4 centimeters) to the full 4 inches (10 centimeters).
The presenting part of the baby, usually the head, begins to descend into the woman's pelvis.
The woman begins to feel the urge to push as the baby descends, but she should resist it.
This phase averages about 5 to 7 hours in a first pregnancy and 2 to 4 hours in subsequent pregnancies.
SECOND STAGE
From the complete opening of the cervix to delivery of the baby. This stage averages about 45 to 60 minutes in a first pregnancy and 15 to 30 minutes in subsequent pregnancies. During this stage, the woman pushes.
THIRD STAGE
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.
Start of Labor: All pregnant women should know what the main signs of the start of labor are:
Contractions in the lower abdomen at regular intervals
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:
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.
Rupture of membranes: Occasionally, the fluid-filled membranes that contain the fetus (amniotic sac) rupture before labor starts, and the amniotic fluid flows out through the vagina. This event is commonly described as "the water breaks."
When a woman's membranes rupture, she should contact her doctor or midwife immediately. About 80 to 90% of women whose membranes rupture before but 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 Some Trade Names
