What is childbirth?

Process and Effects

In humans, pregnancy lasts an average of forty weeks, counting from the first day of the woman’s last menstrual cycle. Actually, ovulation, and therefore conception and the start of pregnancy, does not normally occur until about two weeks after the beginning of the last menstrual period, but because there is no good external indicator of the time of ovulation, obstetricians and other health care providers typically count the weeks of pregnancy using the easily observed last period of menstrual bleeding as a reference point. Because of the uncertainty about the actual time of ovulation and conception, the calculated due date for an infant’s birth may be inaccurate by as much as two weeks in either direction.

There is incomplete understanding of the processes that determine the timing and initiation of childbirth. Near the end of pregnancy, the uterus undergoes changes that prepare it for the birth process: The cervix softens and becomes stretchy, the cells in the uterus acquire characteristics that enable them to contract in a coordinated fashion, and the uterus becomes more responsive to hormones that cause contractions.

A number of substances are involved in the preparation of the uterus for birth, including the hormones
estrogen and progesterone (produced within the placenta), the hormone relaxin (from the maternal ovary and/or uterus), and
prostaglandins (produced within the uterus). The fetus participates in this preparation, since it provides precursors necessary for the uterine synthesis of estrogens. In addition, the amnion and chorion (the placenta and umbilical cord), two membranes surrounding the fetus, are capable of producing prostaglandins that assist in the preparation of the uterus.

Once labor begins, the hormone oxytocin (from the maternal pituitary gland) and uterine prostaglandins cause uterine contractions. It is not known what triggers the onset of labor or how the preparatory hormones and prostaglandins work together. However, a 2009 study indicated that labor may be triggered by elevated levels of placental corticotrophin-release hormone (CRH), which promotes the production of a steroid hormone called DHEAS by the fetal adrenal gland. The placenta is then thought to convert the steroid hormone into estriol, and the increasing imbalance between estriol and estradiol (both estrogens) may be responsible for inducing labor. Typically, estradiol blocks estriol's actions, but as the imbalance between these two estrogens increases, estriol is able to activate proteins in the uterine muscles, which then produce prostaglandins that promote muscle cell contraction.

In humans, the onset of labor is indicated by one or more of three signs: the beginning of regular, rhythmic uterine contractions; the rupture of the amniotic membrane, a painless event that is usually accompanied by the leakage of clear fluid from the vagina; and the expulsion of a slightly bloody mucus plug from the cervix, which is an indication that the cervix is beginning to dilate. These signs may appear in any order, or occasionally one sign may be absent or unnoticed. For example, the amniotic membrane may fail to rupture spontaneously; in this case, the attendant will usually pierce the membrane to facilitate the birth.

Uterine contractions are the most prominent indication of labor, which is divided into three stages. In the first stage of labor, the contractions have the effect of dilating the cervix from its initial size of only a few millimeters to full dilation of 10 centimeters, large enough to permit the passage of the fetus. When the first stage of labor starts, the contractions may be up to twenty minutes apart, with each contraction of relatively short duration. As the first stage progresses, the contractions become longer and closer together, so that by the end of the first stage there may be only a minute between contractions. There is no downward movement of the fetus during the first stage of labor, but the contractions do force the fetus against the cervix, and this force is important in causing cervical dilation. This first stage lasts for an average of eleven hours in women giving birth for the first time, but up to twenty hours is considered normal. The average length of the first stage of labor in women who have previously delivered is reduced to seven hours, with a norm of up to fourteen hours.

In the second stage of labor, the fetus moves downward through the fully dilated cervix and then into the vagina as a result of the force exerted by the continuing uterine contractions. Voluntary contractions of the abdominal muscles by the mother can help shorten this stage of labor by applying additional force, but in the absence of voluntary contractions (as with an anesthetized mother), the uterine contractions are usually sufficient to cause delivery. In approximately 96 percent of human births, the fetus is situated so that the head is downward and thus is first to pass through the birth canal. Because the vagina does not lie in the same line as the cervix and uterus, the head of the fetus must flex and rotate as the fetus progresses downward past the mother’s pelvic bones. The final barrier to the birth of the fetus is the soft tissue surrounding the vaginal opening; once the head of the fetus passes through and stretches this opening, the rest of the body usually slips out readily. The average duration of this second stage of labor in women delivering for the first time is slightly more than one hour; the average duration is shortened to twenty-four minutes in women who have previously delivered. Most women agree that the
actual birth of the child during the second stage is less uncomfortable than the strong uterine contractions that occur at the very end of the first stage of labor, when the cervix is dilating the last centimeter or so.

Most infants begin to take regular, deep breaths immediately upon delivery. These breaths serve to inflate the lungs with air for the first time. The infant now becomes dependent on breathing to supply oxygen to the blood, whereas oxygen had been supplied to the fetal blood by circulation through the placenta.

Following delivery of the infant, the mother enters the third stage of labor, during which continued uterine contractions serve to reduce the size of the uterus and expel the placenta. The placenta usually separates from the uterus and is expelled five to fifteen minutes after the birth of the infant.

Uterine contractions do not end with the delivery of the placenta; they continue, with decreasing frequency and intensity, for as long as six weeks following childbirth. These later contractions, known as afterpains, serve to reduce bleeding from the site of placental attachment and to return the uterus and cervix to their prepregnancy condition.

Another significant process that occurs in the mother’s body following delivery is the onset of milk production. During pregnancy, the breasts are prepared for later milk production by a number of hormones, but actual milk production does not begin until about the second day after delivery. It appears that the decrease in progesterone levels caused by the removal of the placenta at birth allows milk production to commence.

Most obstetrical attendants agree that the ideal childbirth situation is a labor and delivery with a minimum of medical intervention. If all goes well, the role of the attendant will be primarily that of a support person. Most women are admitted to a hospital or birthing center during the first stage of labor. The mother’s blood pressure and temperature will be checked frequently. In addition, the strength and timing of contractions will be assessed either by a hand placed lightly on the abdomen or by an electronic monitor that detects uterine activity through a sensor belt placed around the abdomen. The fetal heart rate will be measured with a stethoscope or by this same electronic monitor placed on the mother’s abdomen. Fetal well-being may also be monitored by an electrode placed on the scalp of the fetus through the cervix. This scalp pH probe indicates whether the fetus is tolerating labor well or is in distress. Cervical dilation can be assessed by a vaginal examination: The attendant will insert one or more fingers into the cervix to determine its state of dilation. It is also important that the attendant provide emotional support and reassurance to the mother throughout the delivery.

During the second stage of labor, the attendant will monitor the progress of the fetus through the birth canal. By inserting a hand into the vagina and feeling for the fetal skull bones, the attendant can determine the exact placement of the fetus within the birth canal. As the infant’s head appears at the vaginal opening, an incision called an
episiotomy is usually performed to prevent accidental tearing of these tissues. Many physicians believe that episiotomy should be done to prevent possible vaginal tearing, since a planned incision is easier to repair than an accidental tear. Another advantage of episiotomy is that it tends to speed the expulsion of the infant, which may be an advantage to both the mother and the child at this stage. The episiotomy incision is made after the injection of a local anesthetic to numb the area, and the incision is stitched closed following the delivery of the placenta.

Once the infant’s head has emerged from the vagina, the attendant uses a suction device to clear the infant’s nose and mouth of fluid. As the rest of the infant emerges, the attendant supports the body; a quick examination is conducted at this time to determine whether the infant has any major health problems. The umbilical cord that joins the infant to the placenta is usually cut within a few minutes after birth. When the placenta is delivered, the attendant will examine it for completeness and then will perform a thorough examination of the mother and child to ensure that all is well.

Complications and Disorders

If the labor and delivery do not progress normally, the attendant has available a number of medical interventions that will promote the safety of both the mother and the baby. For example, labor may be induced by administration of oxytocin through an intravenous catheter. Such induction is performed if the amniotic membrane ruptures without the spontaneous onset of uterine contractions, if the pregnancy progresses well beyond the due date, or in response to maternal indicators such as hypertension. The induction of labor has been found to be safe, but careful monitoring of the progress of labor is required.

Another fairly common procedure is the use of forceps to assist delivery. These tonglike instruments have two large loops that are placed on the sides of the fetal head when the head is in the birth canal. Forceps are not used to pull the fetus from the birth canal; instead, they are used to guide the fetus through the birth canal and to assist in the downward movement of the fetus during contractions. The use of forceps can help to speed the second stage of labor, and injury to the fetus or the mother is minimal when the forceps are not applied until the fetal head is well within the birth canal, as is the convention. Some type of anesthesia is always used with a forceps delivery. In some areas, vacuum extraction of the fetus is preferred. As the name implies, vacuum extraction makes use of a suction cup on the end of a vacuum hose; the suction cup is affixed to the fetal scalp.

Many women require some type of pain relief during labor, although this need can be reduced by thorough education and preparedness during the pregnancy. A wide range of pain-reducing drugs (analgesics), sedatives, and tranquilizers is available for use during the first stage of labor. These are typically administered by injection; they work at the level of the brain to alter the perception of pain and to promote relaxation. The goal is to use the minimum drug dose that allows the woman to be comfortable. The main danger is that these drugs reach the fetus through the placental circulation; side effects in the infant, which can persist for many hours after delivery, may include depressed respiration, irregular heart rhythm or rate, and sleepiness accompanied by poor suckling response.

Anesthetics that numb pain-carrying nerves in the mother may also be used during the first and second stages of labor. Two routes of delivery are in common use: epidural and spinal, both of which involve the injection of anesthetic drugs into or near the membranes around the mother’s spinal cord. The epidural route of injection places the anesthetic in a space that lies outside the spinal cord membranes; with spinal anesthesia, the injection is made slightly deeper into the membranous layers. An advantage of both methods is that the mother remains awake during the delivery and can assist by pushing during the second stage.

Although the disadvantages of both anesthetics, and especially of epidurals, have been downplayed, these procedures do impose restrictions on the mother. Once an epidural has been given, for example, a woman must stay in bed because it will be difficult for her to move her legs; some hospitals do offer “mobile epidurals,” which use a type of drug that blocks the pain while still allowing the woman to walk around, but these are the exception. Because walking helps to stimulate labor, the use of epidurals can be counterproductive. The use of epidurals is also associated with a prolongation of the second stage of labor and with increased need for forceps to assist delivery. Headaches, backaches, low blood pressure, nausea, and other side effects may result in the mother following the use of anesthetics. Moreover, contrary to past evidence, recent studies have suggested that the drugs in epidurals do cross the placenta to the baby, causing health risks.

General anesthesia refers to the use of drugs that induce sleep; they may be administered by inhalation or by injection. Because of profound side effects in both the mother and child, most physicians use general anesthesia only in an emergency situation requiring an immediate cesarean section.

Cesarean section refers to the delivery of the fetus through an incision made in the mother’s abdominal and uterine walls. (The name derives from an unsubstantiated legend that Julius Caesar was delivered in this way.) Cesarean deliveries may be planned in advance, as when a physician notes that the fetus is in a difficult-to-deliver position, such as breech (buttocks downward) or transverse (sideways). Multiple fetuses may also be delivered by cesarean section in order to spare the mother and her infants excessive stress. Alternatively, cesarean delivery may be performed as an emergency measure, perhaps after labor has started. As fetal monitoring techniques have improved, problems are noted more quickly and with greater frequency, leading to a larger number of cesarean sections. One indication of the need for emergency cesarean delivery is fetal distress, a condition characterized by an abnormal fetal heart rate and rhythm. Fetal distress is thought to be an indication of reduced blood flow to the placenta, which may be life-threatening to the fetus. Cesarean section may be performed using spinal or epidural anesthesia, as well as general anesthesia. A woman who delivers one child by cesarean section does not necessarily require a cesarean for later deliveries; each pregnancy is evaluated separately. Attempted vaginal births after cesareans (AVBACs) are still being done but are decreasing in frequency due to increased likelihood of problems.

Perspective and Prospects

Prior to 1800, most women were attended during childbirth by female midwives. In some areas, a midwife was provided a salary by the town or region; her contract might stipulate that she provide services to all women regardless of financial or social status. In other areas, midwives worked for fees paid by the clients. Midwives of this time had little, if any, formal training and learned about birth practices from other women. Because birth was considered a natural event requiring little intervention on the part of the attendant, the midwife’s medical role was limited and the few doctors available were consulted only in difficult cases. Although birth statistics were not kept at the time, anecdotal accounts from the diaries of midwives and doctors suggest that the births were most often successful, with rare cases of maternal or infant deaths.

The nineteenth century saw a gradual shift away from the use of midwives to a preference for formally trained male doctors. This shift was made possible by the establishment of medical schools that provided scientific training in obstetrics. Because these schools were generally closed to women, only men received this training and had access to the instruments and anesthesia that were coming into use.

Maternity hospitals came into being during the nineteenth century but were at first used primarily by poor or unmarried women. Women of higher social status still preferred to deliver their children in the privacy of their homes. Indeed, home birth was safer than hospital birth, since the building of hospitals had outpaced the knowledge of how to sanitize them. Rates of infection and maternal and infant death were higher in hospitals than in homes.

By the 1930s, the situation had reversed: Hospital births had become safer than home births, because sanitation and surgical procedures had improved. There followed an increasing trend for women to enter hospitals for delivery, so that the percentage of women giving birth in hospitals increased from about 25 percent in 1930 to almost 100 percent by 1960. In the same period, maternal and infant mortality showed a dramatic reduction. The shift to hospital birth had coincided with an interventionist philosophy: Most women were anesthetized during delivery, and forceps deliveries and episiotomy became more common.

By the 1960s, the older idea of “natural” childbirth—that is, a birth that encourages active labor and the use of drug-free types of pain relief with as little medical intervention as possible—had regained popularity. This change in attitude was brought about in part by recognition that analgesic and anesthetic drugs often had profound effects on the infant and often prevented strong mother-infant bonding in the immediate hours after delivery.

It was also brought about by the Lamaze method of childbirth, conceived by French doctor Fernand Lamaze and introduced to the United States with Marjorie Karmel’s book Thank You, Dr. Lamaze (1959). In this method, women learn controlled breathing techniques to relax and to cope with contractions during labor. A labor coach, who is often the baby’s father, helps to initiate and facilitate these techniques. Because natural childbirth must be learned, usually through childbirth classes offered in hospitals during the last trimester of pregnancy, it is also called prepared childbirth. As an extension of natural childbirth, the LeBoyer method has been proposed, allowing for delivery to take place underwater, so that the fetus is expelled from the fluid-filled amniotic sac into a warm, peaceful, fluid-filled environment, allowing for an easier transition to extrauterine life.

By the latter part of the twentieth century, a compromise between the more radical approaches of the past seemed to have been reached, with common practice in obstetrics being to allow the birth to proceed naturally when possible, but with the advantage of having refined drugs, diagnostics, and surgical techniques available if needed. The midwife has been reinstated as a specially trained advanced practice nurse (certified nurse midwife) who provides comprehensive health care to pregnant and nonpregnant women, and who conducts deliveries under a variety of settings, collaborating with physician colleagues as necessary for medically complicated labor and birth.

Bibliography

Ammer, Christine. The New A to Z of Women’s Health: A Concise Encyclopedia. 6th ed. New York: Checkmark Books, 2009.

Beckmann, Charles R. B., et al., eds. Obstetrics and Gynecology. 7th ed. Baltimore: Lippincott Williams & Wilkins, 2013.

Creasy, Robert K., et al., eds. Creasy & Resnik's Maternal-Fetal Medicine: Principles and Practice. 6th ed. Philadelphia: W. B. Saunders, 2008.

Cunningham, F. Gary, et al., eds. Williams Obstetrics. 23d ed. New York: McGraw-Hill, 2010.

DeCherney, Alan, et al., eds. Current Diagnosis & Treatment: Obstetrics & Gynecology. 11th ed. New York: McGraw Hill, 2012.

Klaus, Marshall H., John H. Kennell, and Phyllis H. Klaus. Doula Book: How a Trained Labor Companion Can Help You Have a Shorter, Easier, and Healthier Birth. 2d ed. Reading, Mass.: Perseus, 2002.

Klein, M. C., et al. “Why Do Women Go Along with This Stuff?” Birth 33, no. 3 (September, 2006): 245–250.

"Labor and Birth." US Department of Health and Human Services Office on Women's Health, September 27, 2010.

Lees, Christoph, and Grainne McCarten. Pregnancy and Birth: Your Questions Answered. Rev. ed. New York: DK, 2012.

Quilligan, Edward J., and Frederick P. Zuspan, eds. Current Therapy in Obstetrics and Gynecology. 5th ed. Philadelphia: W. B. Saunders, 2000.

Simkin, Penny, et al. Pregnancy, Childbirth, and the Newborn: The Complete Guide. 4th ed. Minnetonka, Minn.: Meadowbrook Press, 2010.