For 9 months, the unborn child has been developing within the womb. Now the fetus is prepared to make an exit. Birth in human beings typically occurs 270 days after conception, near the end of a full 9 months. Shortly before birth (typically a few weeks for first births but sometimes only a few hours for later pregnancies), the fetus usually rotates into a head-downward position. This movement is referred to as lightening because it releases pressure on the mother's abdomen. For women giving birth for the first time, labor will usually last between 12 and 24 hours, with an average of 14 hours. However, for women who have given birth before, labor usually averages only 6 hours.
First StageQuestion: What are the first signs of labor?
Labor is commonly divided into three stages that typically overlap each other. During the first stage, which lasts, on the average, about 13 hours for a woman having her first child, uterine contractions begin. It was discovered that the levels of a certain enzyme increase dramatically as labor starts. This enzyme chews up the collagen that holds together the fetal membrane, which in turn causes the amniotic sac to rupture (commonly referred to as the time when a woman's "water breaks.") The ensuing contractions associated with the rupture are usually spaced from 10 to 20 minutes apart. Initially the contractions are gentle, but they tend to become more powerful and sometimes uncomfortable.
Question: When should the mother go to the hospital?
Some mothers prefer not to use hospital facilities and instead give birth at home, usually with a midwife or physician present to help with the delivery. However, from 10 to 15 percent of deliveries do require special help. For this reason, unless complete facilities can be made available in the home, doctors usually recommend that mothers be in the hospital or other birthing facility within a few hours after the beginning of labor.
The second stage of labor usually lasts about 90 minutes. During this stage, the cervix opens sufficiently and the baby begins to move down the birth canal. At this point, if the mother has been well prepared, she may use her abdominal muscles to help push the baby along. This second stage of labor may often be shortened considerably by having the mother give birth in a vertical position, for example, by using a bed or room especially designed to include a birthing bar. When the mother is upright, gravity helps the baby move down the birth canal. Although the second stage of labor usually takes about 90 minutes, the average time in an upright position is only 30 minutes. At the end of the second stage of labor, the baby is born.
During birth, the human fetus is forced through the birth canal under extreme pressure and is intermittently deprived of oxygen. During this time, the baby secretes the hormones adrenaline and noradrenalin, collectively classified as catecholamine, at levels that are higher than they are likely to be at any other time throughout his or her life. Adrenaline helps open up the lungs, dry out the bronchi, and thus achieve the switch from a liquid to an air environment. Noradrenalin, which is especially prevalent, slows the heartbeat, enabling the fetus to withstand fairly lengthy oxygen deprivation. Babies delivered by Cesarean section, which we will discuss shortly are brought out of the mother surgically and do not pass through the birth canal. Interestingly these infants often have respiratory problems. One reason for such problems might be that the infant has not benefited from the usual stress of birth!
Question: Are all babies born in the head-first position?
About 97 percent of babies are born in the head-first position. The fetus's skull is soft and pliable, which helps the head to pass through the birth canal. However, 2.4 percent of babies are born rump first; this is called a breech birth. During a breech birth, great care must be taken to avoid damage to the baby's head, which is the most difficult part of the infant's body to pass through the birth canal.
An even rarer occurrence is the shoulder presentation. This occurs in only 1 birth out of 200. The shoulder presentation is extremely dangerous because the baby must be forced by the attendants into a breech position. This forcing can rupture the uterus, which may cause the death of the infant and severe hemorrhaging in the mother.
Another dangerous problem that can occur during birth is anoxia. Anoxia can occur if the placenta detaches prematurely if the umbilical cord is pinched or tangled, if the infant's head is injured to the point of hemorrhaging, or if the mother has been too heavily sedated during labor. If there is a problem during birth, the child may be removed from the uterus by Cesarean section. Approximately 23% of all births in the United States are Cesarean sections. In this procedure, the mother's abdomen is opened surgically and the baby is removed without passing through the vaginal canal. The surgical incision is then closed as it would be after any other surgical procedure.
Whenever possible, obstetricians use special surgical incisions in the uterus so that a woman who has had one Cesarean section may later deliver babies vaginally. With the old Cesarean technique (when a vertical incision was used), once the incision was made and the uterine wall weakened, it was necessary to have any future babies also delivered by Cesarean. It should be noted, however, that women giving birth vaginally for the first time should expect labor to last as long as a typical first-time labor, regardless of how many babies they may have previously had by Cesarean section.
In addition, some obstetricians have recommended that Cesarean sections not be used routinely if breech birth or labor problems begin. They argue that breech births for low-weight babies, especially if the obstetrician is skilled, may present no difficulty and that abnormal labor of and by itself is not sufficient cause for a Cesarean section. When it is necessary, however, Cesarean section can be a lifesaver for both infant and mother.
Following the birth of the infant, the third stage of labor occurs, during which the placenta is expelled. The placenta and other expelled materials are called the afterbirth.
Source: "CHAPTER 3 CONCEPTION, PRENATAL DEVELOPMENT, AND BIRTH," Introduction to Child Development, 6th ed., John Dworetzky, West Publishing Company, San Francisco, CA, 1996.