Pregnancy is a normal physiologic process which begins with conception, follows through development and growth of the fetus and delivery, and ends with return to a fully normal state approximately 6 weeks after birth. Pregnancy causes physiologic changes in the mother's bodily functions to allow for growth and development of the fetus. For the fetus, pregnancy is a time of dependency on the mother for nutrition and, thus, exposure to whatever agents to which the mother is exposed. Although a healthy pregnancy is normal for the majority of women, for some there may be complications that can lead to adverse outcome for the mother or the fetus. The average biological length of human gestation, from conception to delivery, is 266 days. Due to the difficulty in assessing the exact date of conception, however, the clinical length of pregnancy is considered to be 280, days or 40 weeks, calculated from the last normal menstrual period before the cessation of menses, or menstrual flow. This calculation assumes that ovulation occurs 14 days after the last menstrual period. Human gestation is further divided into trimesters, each of which lasts slightly more than 13 weeks. FETAL DEVELOPMENT After the ovum, or egg, is fertilized by a sperm (see \Tfertilization\t; \Treproductive system, human\t), the fertilized ovum becomes implanted in the uterus. First Trimester Most fetal development, with the exception of such complex functions as brain development, occurs in the first trimester. The heart begins to beat after 4 weeks. By 8 weeks, the eyes, ears, nose, mouth, fingers, and toes are easily recognizable, and male and female reproductive systems have differentiated. By 12 weeks, all of the recognizable organs have developed. During these first weeks the fetus is most vulnerable to potential teratogenic or birth-defect-inducing agents, such as drugs, radiation, and viruses. Drugs taken in by the mother during the first weeks can be of particular harm, demonstrated in Europe in the late 1950s when the drug \Tthalidomide\t, commonly administered to treat nausea and vomiting, was found to be associated with congenital malformations. Second Trimester During the second trimester, thin-walled skin develops, organs begin to function, and blood begins to be formed in the bone marrow. In addition, scalp hair appears, subcutaneous fat increases, and bones begin to harden. Although the fetus begins to move in the first trimester, it is not until about 20 weeks gestation that the mother begins to perceive the movements, the onset of which is called "quickening." Third Trimester The majority of fetal weight gain occurs in the third trimester. Ear lobes begin to develop cartilage, testes begin to descend into the scrotum, nails begin to grow over the tips of the digits, and creases develop over the soles of the feet. In addition, the fetus begins to demonstrate coordinated patterns of behavior that are similar to the cycles of wakefulness and activity of a newborn. THE PREGNANT BODY A woman's body undergoes a variety of changes to prepare for the growth, nourishment, and birth of a child. First Trimester An early sign of pregnancy is the cessation of menses, which occurs due to the rising levels of human chorionic gonadotrophin (HCG), a hormone produced by the placenta (see \Tpregnancy test\t). The first trimester is characterized by a number of common discomforts. Nausea and vomiting may begin at approximately eight weeks gestation. Increased urinary frequency is common due to the pressure of the enlarging uterus on the bladder. Breast soreness or tingling often occurs due to hormonal stimulation. Fatigue is also a common complaint. Second Trimester Increasing abdominal girth and pressure from the growing uterus can lead to constipation. Normal intermittent uterine contractions, called Braxton-Hicks contractions, may occur. The mother may experience lightheadedness and may even pass out due to the effects of the hormones on the blood vessels and the amount of blood diverted to the uterus, placenta, and fetus. Heartburn becomes an ever increasing problem because of the increasing pressure on the stomach by the enlarging uterus and delayed emptying of the stomach. Despite these discomforts, women are generally more comfortable during the second trimester than the first. Third Trimester The last weeks of pregnancy become increasingly uncomfortable. Headaches, hemorrhoids, varicose veins, and swelling of the legs may occur. Shortness of breath is common due to the enlarged uterus, which prevents full expansion of the lungs. In the last days of gestation increased pelvic discomfort develops, caused by the dropping of the fetal head into the pelvis. False labor pains, or contractions of the uterus that do not lead to progressive dilatation, or opening, of the cervix, can be particularly uncomfortable. Insomnia may also be common in the days before delivery. PRENATAL CARE It is widely accepted that women who receive prenatal care have fewer complications of pregnancy and birth and have healthier babies. It is also known that the earlier and more consistently the care is received, the better the outcome. Education about pregnancy and child-bearing is an important part of prenatal care, as are detection and treatment of abnormalities. Assessment and reassessment of risk to the mother and fetus are inherent in the provision of prenatal care. In fact, the best time to assess many of these risk is before a woman conceives. Therefore, it is becoming popular for child-bearing women to receive preconception care while still planning a pregnancy. These preventative health visits are designed to achieve optimum health from the moment of conception to birth. SPECIAL PROBLEMS IN PREGNANCY Although it is a normal process, some women have severe problems during pregnancy. The maternal mortality rate is the number of maternal deaths occurring per 100,000 live births. In most Western countries this number is as low as 10 deaths per 100,000 live births. In developing countries, however, maternal mortality rates can be as high as 1,000 per 100,000 live births. It is estimated that in the 1980s, approximately 500,000 women worldwide died every year from pregnancy-related causes. These deaths were related to either direct causes where the pregnancy itself or pregnancy complications led to maternal complications; or indirect causes where the pregnancy aggravated a maternal condition such as diabetes or heart disease. Problems of pregnancy include the following. Spontaneous Abortion Anywhere from 10 to 40 percent of human pregnancies end in miscarriage, or spontaneous abortion. Often, increased vaginal bleeding and cramping occurs around the time of a normal menstrual period and may go unnoticed by the woman. Genetic analysis of this material suggests that at least 50 percent of these spontaneous miscarriages are due to major chromosomal abnormalities. Ectopic Pregnancy A pregnancy that occurs at a site other than inside the uterus, such as in the fallopian tube, on the ovary, or at sites outside the abdomen, are termed ectopic. Such pregnancies are generally not viable and can in fact be life threatening to the mother. Infectious Diseases A variety of infectious diseases, especially \TGerman measles\t (rubella), \Ttoxoplasmosis\t, and \Tchicken pox\t, can lead to abnormalities of fetal growth and development. Some venereal diseases can be transmitted to the fetus, particularly gonorrhea, syphilis and Acquired Immunodeficiency Syndrome (\TAIDS\t). Routine tests are conducted before and during pregnancy to test for these infections and, if possible, treat them before harm is done to the fetus. Rh Disease The \TRh factor\t is a specific antigen located on red blood cells. If a mother has Rh negative blood and carries an Rh positive child, there is a possibility that the Rh positive blood cells of the child will cross the placental barrier, triggering antibody production to the Rh factor in the mother. These maternal antibodies may attack the blood of a subsequent Rh positive fetus, causing a severe and often fatal type of anemia. Doctors are now able to prevent Rh disease with a vaccine. Once common, the disease is now a rare problem and its eradication is one of the major triumphs of modern obstetrics. Diabetes \Tdiabetes\t, or glucose intolerance, is a common complication of pregnancy. Diabetic women develop an increase in their insulin requirements when pregnant, which often makes their diabetes difficult to control. The outcome for these mothers and babies is significantly impaired. For instance, maternal high blood sugar leads to very large babies. In cases where diabetes is advanced, kidney and placental impairment may occur, which also may lead to fetal growth problems. Glucose intolerance that develops during pregnancy is called gestational diabetes. It can be managed with diet alone, or in combination with insulin. Hypertension Women who have chronic hypertension, or high blood pressure, have an increase in complications of pregnancy, particularly kidney disease. In addition there are certain hypertension diseases that can develop during pregnancy. The causes of these diseases are poorly understood, and as a result they are given many names including pregnancy-induced hypertension, toxemia, preeclampsia, or EPH gestosis. These diseases are characterized by protein in the urine and swelling or edema that can lead to seizures, liver damage, kidney damage, bleeding abnormalities, and poor fetal growth and outcome. Anemia Anemia, or a low blood cell count, is common during pregnancy. Women often have a chronic iron-deficiency anemia before pregnancy due to monthly blood loss from menstruation. During pregnancy this is compounded by the increased nutritional requirements to support the fetus. In addition to iron deficiency anemia, there are also other deficiency states that commonly cause anemia, such as vitamin B deficiency. In developing countries, anemia due to malaria is a major cause of morbidity. Pregnancy over Age 35 It is becoming an increasingly common event for women over age 35 to become pregnant. Generally, these women do well if they were in good health prior to the pregnancy. Certain conditions are more common in older pregnant women, however, such as hypertension and gestational diabetes. In addition, for each year over the age of 35, there is an increased risk of giving birth to a child with chromosomal anomalies, such as \TDown's syndrome\t. This risk increases to 1 out of every 38 births by the age of 44. A variety of prenatal chromosomal diagnostic tests are available for older pregnant women. Poor Nutrition It is ideal for the growing fetus if the mother gains at least 25-30 pounds during her pregnancy. Low prepregnancy weight or low weight gain, particularly if food is low in protein, vitamins, and minerals, can impair fetal growth at the time when brain cells are rapidly developing. Smoking, Alcohol, Drugs Smoking during pregnancy affects fetal growth and development due to increased carbon monoxide and decreased oxygen in the blood. Heavy drinking of alcohol impairs the mother's nutrition and can cause damage to her liver. In addition, the fetus can develop \Tfetal alcohol syndrome\t, a cluster of mental and physical birth defects. The use of such drugs as marijuana, amphetamines, cocaine, and heroin all adversely affect the fetus. Babies are smaller, sicker, and more likely to be stillborn. In addition, babies born to women who used drugs during pregnancy may be addicted to the drug at birth. Cocaine is a particularly dangerous drug during pregnancy because it constricts the blood flow to the developing fetus. (see also \Tbirth defects\t.) TESTS OF FETAL WELL-BEING Since the development of electronic fetal monitoring and the proliferation of the field of genetics in the late 1960s, prenatal tests of fetal well-being have evolved. In addition to these highly technical tests, the value of some basic techniques, such as the mother counting fetal movements, are being used more often. Amniocentesis During an \Tamniocentesis\t, a sample of the amniotic fluid surrounding the fetus is obtained. This fluid contains cells from the fetus that can be cultured, or grown, to determine chromosomal makeup, fetal lung maturity, and other information about the fetus. Amniocentesis carries a risk of fetal-death of less than 1 percent, particularly when performed by skilled practitioners. Chorionic Villus Sampling (CVS) In this procedure, a small amount of tissue is removed from the fetus at 9-10 weeks gestation. The genetic material of the tissue sample is tested for chromosomal abnormalities. The advantage of this technique is that it can be performed very early in pregnancy, and the results are generally available before the end of the first trimester. The risks of fetal death due to the procedure are about the same as those of amniocentesis, or approximately 1 percent. Percutaneous Umbilical Blood Sampling During this procedure, also known as cordocentesis, blood is obtained directly from the umbilical cord using ultrasound guidance. Chromosomal and biochemistry tests can be performed on this pure fetal blood sample. These results can be available within minutes to hours. This relatively new procedure carries a higher risk of fetal loss than those above, somewhere in the range of two to five percent. Fetal Monitoring Techniques Electronic fetal monitoring has become commonplace in the evaluation of fetal well-being. Tracings of the fetal heart rate and uterine activity are used to evaluate the response to contractions, fetal movement, or external stimuli. These tests are begun after 28 weeks gestation, the time in pregnancy when a fetus has a reasonable chance of living outside the uterine environment, if that environment is determined to be potentially dangerous. The nonstress test, which evaluates the fetal heart-rate response to fetal movement, is the most common method of antepartum (prebirth) screening for well-being. If the fetus is in some jeopardy, there will be no characteristic accelerations of the fetal heart rate accompanying fetal movement. Another common antepartum screening test is the contraction stress test. Contractions of the uterus are stimulated and the fetal heart rate response is monitored. Decelerations in the heart rate during the contraction indicates that the placenta does not have an adequate reserve of oxygen to supply the fetus. Ultrasound Ultrasound has become an integral part of the evaluation and treatment of pregnancy. Sound waves are passed over the maternal abdomen, and images of the fetus and surrounding tissues are observed on a viewing screen. Ultrasound monitors the growth of the fetal head, limbs, kidneys, liver, lungs, and brain. The technique can also be used to evaluate fetal movement, breathing, and the amount of amniotic fluid and the condition of the placenta. Information gained from the use of ultrasound is useful throughout pregnancy to determine gestational age, the presence of more than one fetus, any fetal malformations and defects, and the position of the fetus and placenta. Fetal Surgery Fetal surgery has been performed to correct fetal kidney obstruction, fetal hydrocephalus, and diaphragmatic hernia. Fetal surgery is beneficial only to a small number of fetuses and the procedure is still considered experimental. \Tbirth\t The onset of labor is a complex neuroendocrine event involving the release of the hormone oxytocin from the baby's pituitary gland into the maternal circulation. This hormone stimulates uterine contraction. Labor Labor is divided into three stages. The first stage begins at the onset of regular contractions which cause progressive dilatation of the cervix. The latent phase of this stage is from the start of labor to approximately 4 cm dilatation, and the active phase is from the end of the latent phase to approximately 10 cm dilatation. The second stage of labor begins at the onset of complete dilatation and continues to the birth of the baby. The third stage of labor begins at the birth of the baby and continues through the expulsion of the placenta. In general, the contractions of the uterus get progressively stronger and closer together over the course of labor. COMPLICATIONS OF BIRTH Most often, pregnancy and birth results in an uncomplicated spontaneous vaginal delivery. However, complications of labor and birth may occur, many of which can pose serious problems for the mother or fetus or both. Premature Labor and Birth Premature labor is defined as labor that begins before the 37th week of pregnancy. Warning signs of preterm labor include mild menstrual-like cramps, low backache, pelvic pressure, increased vaginal discharge or light bleeding, and diarrhea. A prompt exam will determine if preterm labor exists and if it should be treated with medications in an attempt to stop labor. Depending on gestational age, preterm birth frequently leads to respiratory distress, leading to a large proportion of neonatal (newborn) deaths. Due to the danger to the fetus, every attempt is made to recognize and stop preterm labor. Premature Rupture of the Membranes Rupture of the amniotic fluid sac occurring prior to the onset of labor in a pregnancy of any gestation is considered premature rupture of the membranes. This may pose danger to the mother and baby due to the possibility of infection and preterm birth. Labor is sometimes induced if the pregnancy is far enough along, and at other times the woman is placed at rest in the hospital or home to reduce the risk of infection and prematurity. Malpresentation About 96 percent of babies are born head first. Approximately 3 percent are born breech, with the buttocks and legs delivering first, and these babies may be delivered vaginally or by \Tcesarean section\t. About 1 percent of babies are born in a transverse (sideways) position. These babies must be delivered by cesarean. Whatever method of delivery is used, malpresentations pose added risk to the mother and fetus. Disorders of Labor Deviation from the expected progress of labor may result in abnormal patterns of labor contraction, dilatation of the cervix, or descent of the fetus through the pelvic passage. Many disorders are treated by administration of a contraction inducing drug called Pitocin. Other ways of managing labor disorders include maternal rest, maternal and fetal position change, and occasionally the administration of anesthesia. If treatment is unsuccessful, operative delivery is almost always necessary. Pregnancy-Induced Hypertension (PIH) PIH is also known as preeclampsia or toxemia of pregnancy. The symptoms include swelling or edema, high blood pressure, and protein in the urine. When unrecognized or untreated in pregnancy it can be life threatening to the mother and the fetus, but when treated early it can be well controlled. Placenta Previa The placenta normally implants itself at the top of the uterus. When it implants lower in the uterus, near or over the cervix, it can cause mild to severe bleeding during the last half of the pregnancy or during labor. If the placenta covers the entire cervix at the time labor begins, a cesarean delivery is necessary to save the mother and baby. Multiple Births Twins occur once in 80 births, triplets once in 10,000, and quadruplets almost one in a million. Recent advances in the use of fertility drugs has increased the incidence of multiple births. Multiples are more likely to be born prematurely and these pregnancies are consequently at higher risk for complications as compared to single infant births. Chorioamnionitis/Endometritis Chorioamnionitis is an infection of the chorion of the placenta that may spread to surrounding maternal and fetal tissues. It is characterized by maternal fever, increased maternal and fetal heart rate (tachycardia), and uterine tenderness. In about 95 percent of cases, the infection also affects the fetus and can be life threatening. Endometritis is an infection of the uterine lining and is the most common cause of postpartum infection. It is common in women with chorioamnionitis and most common in women delivered by cesarean. Although both conditions are very serious, if recognized promptly, they can be effectively treated with antibiotics. In addition to these complications of birth, emergencies can occur during labor, such as placental detachment before birth (abruptio placenta), worrisome changes in the fetal heart rate (fetal distress), and the umbilical cord slipping in front of the fetal head (cord prolapse), any of which often lead to an operative birth. Operative Delivery Close to one-fourth of all births in the United States are born by cesarean section, the surgical delivery of a baby through the maternal abdomen. A cesarean, when needed, can be a life-saving measure for the mother or the baby. Reasons for a cesarean include: cephalopelvic disproportion (baby is too large for mother's pelvis), transverse lie, fetal distress, prolapsed cord, failure to progress in labor, active genital herpes, and maternal diseases such as preeclampsia, diabetes, or heart disease. The number of cesarean sections performed in the United States has increased in recent years and there is growing concern that many of these operative deliveries were unnecessary. Recent studies have demonstrated that many women who have had a cesarean may safely give birth vaginally in a subsequent delivery. These vaginal births after cesarean (VBACs) are becoming more popular and should help decrease the cesarean birth rate. Other operative deliveries can be conducted using forceps or a vacuum extractor. These techniques are used most often to "lift" the baby out of the birth canal during the very last stages of labor. Using proper technique, these procedures can be very safe for mother and baby but are used only when a reason exists to justify their use. MODERN BIRTH PRACTICES A variety of health care professionals are involved in providing care to women during pregnancy. These include nurses, nurse-practitioners, nurse-midwives, family physicians, obstetricians, and perinatologists. There is no doubt that some women who are at very high risk for pregnancy complications must be under the care of a physician. However, most pregnant women who are healthy with normal pregnancies can receive care from midwives with appropriate consultation from physicians. The role of other health professionals such as dieticians and social workers is also valued in providing optimum resources. Over the years there has been an increased emphasis on childbirth as an experience to be shared in some way with the entire family. This has given rise to alternatives in the location and the way in which birth has been handled. Birth can now safely take place outside the hospital, depending on a woman's risk for complication and the training and expertise of the care providers. Approximately 90 percent of all births in the United States occur in the hospital. Birthing centers that create a home like atmosphere and home birth sites for very low risk women account for most of the remaining births. Natural Childbirth Natural childbirth is based on the belief that fear of anticipated pain of childbirth creates body and muscle tensions that in turn make the process more difficult and unnecessarily painful. It is very common for women to attend some type of childbirth preparation class during the latter weeks of pregnancy to prepare for some of the anticipated events. Many techniques are available, but three that are the most common are the Lamaze Method or phychoprophylaxis technique, the Leboyer Technique, or gentle birth technique, and the Bradley Method or "husband coached" technique. Use of any of these methods has the potential to enhance the family's birth experience and lead to a decrease in the amount of analgesia and anesthesia needed for birth. In fact, many women find these techniques all that is necessary for pain management. Pain Relief When pain of labor requires pharmacologic treatment, or when an operative birth is required, several methods of analgesia and anesthesia are available. Narcotics and sedatives are used intravenously or intramuscularly to reduce anxiety and give some pain relief at certain times in labor. Regional anesthesia is also used. General anesthesia is usually used for obstetrics and includes various combinations of barbiturates, narcotics, and muscle relaxants. POSTPARTUM MATERNAL AND CHILD CARE The length of the postpartum period is traditionally six weeks. This is the length of time required for the mother's uterus and other reproductive tissues to return to their former condition. It may take this number of weeks for the woman to return to her previous emotional state and her previous level of vigor as well. For the most part, however, a well rested woman enjoys these early weeks after delivery. Women who give birth in a hospital are usually discharged within two days after a vaginal birth and within 3-4 days after a cesarean birth. During the first weeks of life, the baby adjusts to conditions outside the mother's body. The neonatal period, which extends from birth to 28 days of life, is the time when the baby's feeding (either breast or bottle) and sleep patterns are established. At 28 days of life, the newborn enters the period of \Tinfancy\t, which extends throughout the first year. Timothy R. D. Johnson and Lisa L. Paine Bibliography: Gabbe, S. G., et al., eds., Obstetrics, 2d ed., (1991); Hales, D., and Johnson, T.R.B., Intensive Caring--New Hope for Problem Pregnancies, (1990); MacCartney, Marion, and van der Meer, Antonia, The Midwife's Pregnancy and Childbirth Book, (1990); Russell, K.P. and Neibyl, J.R., Eastman's Expectant Motherhood, 8th ed. (1989).