Childbirth

BIOLOGY

ANATOMY OR SYSTEM AFFECTED: Reproductive system, uterus

ALSO KNOWN AS: Labor and delivery; parturition

DEFINITION: The process whereby a fetus moves from the uterus to outside the mother’s body—a natural event that typically requires no, or minimal, medical intervention

Process and Effects

In humans, pregnancy lasts an average of forty weeks, counting from the first day of the woman’s last menstrual cycle. In fact, 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 healthcare 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 labor and 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 myometrium, the muscular layer of the wall of 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, studies have indicated that labor may be triggered by elevated levels of placental corticotropin-release hormone (CRH), which promotes the production of a steroid hormone called DHEAS and cortisol by the fetal adrenal gland. The fetal liver is then thought to convert DHEAS 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, commonly known as water breaking; and the expulsion of a slightly bloody mucus plug from the cervix, called the bloody show, 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 ten 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 lactation and breastfeeding 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 in the perineum called an episiotomy may be performed to prevent accidental tearing of these tissues, although this procedure is becoming less common as natural tearing has been found to be less extensive and have fewer complications in most cases. Once a routine part of labor and delivery, episiotomy is now only used in certain cases, such as if the baby is in an unusual position, is larger than average (macrosomia), or needs to be delivered quickly. 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 several 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. The attendant will perform an Apgar evaluation on the baby to determine its health, checking the newborn's heart rate, breathing rate, muscle tone, reflexes, and skin color at one minute and five minutes after birth. Newborns then typically receive eye drops to prevent eye infections that they can contract as they pass through the birth canal during delivery. The American Academy of Pediatrics also recommends all newborns receive a shot of vitamin K, which is needed for the blood to clot. Doctors also perform a heel prick to take a tiny sample of the baby's blood to test for disorders such as phenylketonuria (PKU), hypothyroidism, galactosemia, and sickle cell disease. When such disorders are detected immediately after birth, treatment can begin right away, and serious complications are avoided.

Complications

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 the intravenous administration of oxytocin. 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 (typically after forty-two weeks gestation), or in response to maternal indicators such as hypertension. Oxytocin may also be used to induce labor early in cases where the mother has developed preeclampsia, there is insufficient amniotic fluid surrounding the fetus (oligohydramnios), or the mother has a medical condition such as gestational diabetes that could make full-term delivery more risky. The induction of labor has been found to be safe, but careful monitoring of the progress of labor is required. Premature birth occurs when the baby is delivered before thirty-seven weeks gestation.

Another procedure that may be used if labor is not progressing or the baby's safety is at risk during the second stage of labor 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 baby's head through the birth canal and to assist in the downward movement of the fetus during contractions. The use of forceps can help to speed up the second stage of labor and decrease the need for Cesarean section (C-section). Although forceps delivery is generally safe, the procedure can pose some risks to both the mother—such as more severe tears to the vagina than a natural delivery, potentially causing incontinence after delivery—and the baby—such as facial bruising or nerve damage. Some type of anesthesia is used with a forceps delivery. In some areas, vacuum extraction of the fetus is performed instead of forceps delivery. 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 opt for some type of pain relief during labor, although this need can be reduced by education and preparation during pregnancy, such as practicing the Lamaze technique. The goal is to use the minimum drug dose that allows the woman to be comfortable. In some cases, these drugs can 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. Most commonly, women in labor who request pain relief are given an epidural block, a regional analgesic that is administered into the area outside the spinal cord in the lower back; epidurals have minimal or no effect on the baby, although they can limit the mother's movements during labor, prolong the first and second stage of labor, or decrease maternal blood pressure and the baby's heart rate. Alternatively, with a spinal block, the injection is made slightly deeper into the membranous layers. A spinal block is often used before a C-section, forceps delivery, or vacuum extraction.

Cesarean section (C-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 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 emergency 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. Cesarean sections have been essential in reducing perinatal mortality when complications arise during pregnancy, labor, or delivery; however, C-sections pose the risk of breathing problems to the infant and of inflammation, increased bleeding, blood clots, and infection to the mother, and therefore, they should only be used when medically necessary.

A woman who delivers one child by cesarean section does not necessarily require a cesarean for later deliveries; each pregnancy is evaluated separately. Vaginal births after cesareans (VBACs) are possible but may present increased likelihood of problems, and some hospitals will not allow women to attempt a VBAC because they cannot properly handle emergency C-sections. Nevertheless, 60 to 80 percent of women who attempt a trial of labor after a cesarean section have a successful vaginal delivery. Pregnant women who have a high-risk uterine scar or other complications from a previous C-section should not attempt a VBAC.

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 fully anesthetized during delivery, and forceps deliveries, episiotomy, and C-sections 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 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. Natural childbirth, which is often prepared for through childbirth classes offered in hospitals during the last trimester of pregnancy, is also called prepared childbirth. As an extension of natural childbirth, the LeBoyer method allows 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 and into the early twenty-first 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 healthcare to pregnant and nonpregnant women, and who conducts deliveries in a variety of settings, collaborating with physician colleagues as necessary for medically complicated labor and birth. Likewise, many pregnant women hire doulas, or trained professionals who provide physical and emotional support before, during, and after childbirth. Unlike midwives and doctors, doulas do not perform medical tasks but instead maintain focus on the overall well-being of the mother. New methods of natural childbirth have also gained in popularity in the early twenty-first century. These include hypnobirthing, a technique that uses self-hypnosis, relaxation, and breathing techniques to help promote a calm birthing experience, manage pain, and reduce fear during childbirth. Other gentle birthing approaches incorporate elements of mindfulness into the childbirth experience to create a supportive environment for the mother's mental well-being.

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