women s health issues
Labor
Introduction
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: 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. 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. Standing and walking during the first stage of labor can shorten it by more than 1 hour. FIRST STAGE FIRST STAGE From the beginning of labor to the full opening (dilation) of the cervix—to about 4 inches (10 centimeters). Initial (Latent) Phase Contractions are irregular at first but become progressively stronger and more rhythmic. Discomfort is minimal. The cervix begins to thin and opens to about 1 1/2 inches (4 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 12 hours) in subsequent pregnancies. Active Phase The cervix opens from about 1 1/2inches (4 centimeters) to the full 4 inches (10 centimeters). It thins and pulls back (effaces) until it merges with the rest of the uterus. 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. Pushing too early may be unnecessarily tiring and frequently tears the cervix, which then must be repaired. This phase averages about 5 to 7 hours in a first pregnancy and 2 to 4 hours in subsequent pregnancies. SECOND STAGE SECOND STAGE 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. THIRD STAGE 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. 