Labor has traditionally been divided into three stages: the dilation stage, theexpulsion stage, and theplacental stage.
The Dilation Stage
The dilation stage begins with the onset of true labor, as the cervix dilates completely and the fetus begins to move into the cervical canal. This stage is highly variable in length, but typically lasts 8 or more hours. At the start of this period the labor contractions occur at intervals of once every 10-30 minutes, and their frequency increases steadily. Late in the process, the amnion usually ruptures, an event sometimes referred to as “having the water break.”
The Expulsion Stage
The expulsion stage begins as the cervix dilates completely, pushed open by the approaching fetus. During this stage, contractions reach maximum intensity; they may occur at 2 or 3-minute intervals and last a full minute. Expulsion continues until the fetus has completed its emergence from the vagina, a period usually lasting less than 2 hours. The arrival of the newborn infant into the outside world represents birth, or delivery.
If the vaginal canal is too small to permit the passage of the fetus and there is acute danger of perineal tearing, the passageway may be temporarily enlarged by making an incision through the perineal musculature. After delivery, this episiotomy can be repaired with sutures, a much simpler procedure than dealing with the bleeding and tissue damage associated with a potentially extensive perineal tear. If unexpected complications arise during the dilation or expulsion stages, the infant may be removed by cesarean section, or “C-section.” In such cases an incision is made through the abdominal wall, and the uterus is opened just enough to allow passage of the infant’s head. This procedure is performed during 15-25 percent of the deliveries in the United States — more often than necessary, according to some studies. Efforts are now being made to reduce the frequency of both episiotomies and cesarean section.
The Placental Stage
During the placental stage of labor, muscle tension builds in the walls of the partially empty uterus and the organ gradually decreases in size. This uterine contraction tears the connections between the endometrium and the placenta. Usually within an hour after delivery the placental stage ends with the ejection of the placenta, or “afterbirth.” The disruption of the placenta is accompanied by a loss of blood (as much as 500-600 ml), but because the maternal blood volume has increased greatly during pregnancy the loss can be tolerated without difficulty.
Diketik ulang dari textbook Fundamentals of Anatomy and Physiology , 3rd Edition (Frederic H. Martini), hlm. 1129. o?leh Istiana Ilma