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A great deal of public health resources is spent on pregnancy. It is clear that prenatal and neonatal health play a large role in determining the health of a population, and in fact, pregnancy outcomes are often used as an indicator of a nation's health.

EPIDEMIOLOGY OF PREGNANCY

Globally, there are approximately 240 million pregnancies annually. These pregnancies result in 134 million births and 50 million induced abortions, 20 million of which are performed under unsafe conditions. Approximately 6 to 7 million of these 240 million pregnancies occur each year in the United States. These result in about 4 million liveborn babies, over 1 million induced abortions, at least 1 million spontaneous abortions (miscarriages), nearly 100,000 ectopic pregnancies (a pregnancy in which the fetus develops outside the uterus), and about 30,000 fetal deaths.

Of the 4 million babies born in the United States in 1999, 12 percent were born to women under 20 years of age. Approximately 4.5 percent of white teens (ages 15 to 19), 8.1 percent of African-American teens, and 9.3 percent of Hispanic teens gave birth. Since 1991, the teenage birth rate has been declining in the United States, particularly among African Americans, largely because of an increased use of effective contraception.

In 1999, 13 percent of the babies born in the United States were born to women 35 years old and older. The birth rate among this age group increased during the last three decades of the twentieth century, despite the fact that older women have an increased risk for having babies with chromosomal abnormalities (the risk is approximately 1 in 1,000 at age 25, 1 in 200 at age 35, and 1 in 20 at age 45).

About half of all pregnancies are unintended or unplanned, and one in three babies are born to single or unmarried mothers. (Nearly 70% of African-American babies and over 40% of Hispanic babies are born to unmarried mothers.)

Four out of five women who gave birth in 1999 started prenatal care in the first trimester, though this percentage was lower among African-American and Hispanic women. Despite an overall improvement in prenatal care utilization, the proportion of low birthweight (LBW) births and preterm births have been increasing gradually since the mid-1980s. This increase is accounted for, in part, an increase in multiple gestations and the growing number of infants born to women older than 35 years of age.

Of the 1.2 million legal induced abortions performed in 1999, 20 percent were obtained by women less than 20 years old, 60 percent by white women, and 80 percent by unmarried women.

PHYSIOLOGY OF PREGNANCY

A human pregnancy starts when the male sperm fertilizes the ovum (egg) in a woman's Fallopian tube, and it lasts, on average, 266 days. Contraception works by inhibiting the release of the ovum from the ovary (birth control pill, injectible, or subdermal implant), by impeding the release of sperm (vasectomy), by blocking sperm from entering the vagina or cervix (male or female condom, diaphragm, or cervical cap), or by blocking the Fallopian tubes (tubal ligation). Once conception takes place, the fertilized egg travels through the Fallopian tube into the uterus, where it implants about seven days later. The intrauterine device (IUD) impedes such implantation, and medications like mifepristone (RU486) causes the implanted embryo to abort.

A developing human is called an embryo between two and eight weeks after conception; thereafter it is called a fetus until delivery. Development of the major organs begins during the early embryonic period, and interference with this process may result in birth defects. Women taking harmful substances, or women with preexisting diseases like diabetes mellitus, are at increased risk for having babies with birth defects. Because the development of major organs begins during early pregnancy, often before a woman starts prenatal care or realizes that she is pregnant, preconceptional care is recommended for every woman of reproductive age.

Although most major organs are present at the end of the embryonic period, the development of their functions continues well into the fetal period, infancy, and early childhood. Interference with this process may lead to functional deficits. For example, undernutrition during this period of growth has been associated with increased risk for coronary heart disease, and maternal alcohol use during pregnancy has been linked to mental retardation and other birth defects.

Remarkable changes take place in a woman during pregnancy. The heart circulates 40 percent more blood volume to supply nutrients and oxygen to the growing baby, deeper breaths occur and an increased amount of harmful substances are cleansed through the kidneys. Digestion slows down for better absorption or nutrients, which may cause problems such as heartburn and constipation. The baby is sustained in the uterus by the placenta, which serves as the interface between maternal and fetal circulations. Hormones prepare the breasts for lactation, and the immune system is altered so that it does not reject the baby as a foreign body. While most healthy women make these adaptations readily, pregnancy can jeopardize the health, and sometimes the lives, of women who are less healthy and suffer increased stress to the system during pregnancy.

PATHOPHYSIOLOGY OF PREGNANCY

When things go wrong during pregnancy, the health of both mother and baby may be at risk of certain health problems associated with pregnancy.

Infertility. Infertility is defined as failure to conceive following a period of 12 months or longer of unprotected sexual intercourse. In 1988, over 8 million American women 15 to 44 years of age reported an impaired ability to have children. Major causes include endometriosis, poor sperm quality or low sperm count, failure to ovulate, and tubal damage.

Ectopic Pregnancy. An ectopic pregnancy is a pregnancy that has implanted outside of the uterus, most commonly in the Fallopian tubes, which may have been scarred from a previous infection, ectopic pregnancy, or tubal ligation. The growing pregnancy, if not surgically terminated, may rupture the tube, causing hemorrhage. Ectopic pregnancy is a leading cause of maternal deaths among African-American women.

Abortion. Abortion refers to the termination of pregnancy before the twentieth week of gestation (counting from the last menstrual period). Abortion can be spontaneous or induced. Most spontaneous abortions (miscarriages) involve some chromosomal abnormalities; the causes of the rest are not known, but some may be due to exposure to environmental toxins.

Birth Defects. Birth defects are the leading cause of infant death and the fifth leading cause of potential years of life lost. About 3.6 percent of all babies in the United States are born with major birth defects, the most common being cleft lip and palate, Down syndrome, neural tube defect, and congenital heart disease.

Low Birth Weight (LBW). LBW, defined as birth weight under 2,500 grams (5.5 pounds), is the second leading cause of infant death, and the leading cause of infant death among African Americans. Risk factors include short interpregnancy interval, low prepregnancy weight, inadequate weight gain during pregnancy, history of LBW or preterm birth, cigarette smoking, and socioeconomic factors.

Preterm Birth. Preterm birth, defined as delivery before 37 weeks of gestation, may result in major problems, including neurological damage from brain hemorrhage or respiratory distress from immature lungs.

Fetal Death. Fetal death refers to the death of a fetus after 20 weeks of gestation. Major causes include preexisting maternal conditions like diabetes mellitus or hypertension, and premature separation of the placenta from the uterus (placental abruption) as a result of drug use or trauma.

Infant Death. Infant death refers to death of a baby under one year of age. Major causes include birth defects, LBW, and sudden infant death syndrome (SIDS).

Maternal Death. Maternal death is defined as the death of a woman as a result of her pregnancy, from the first stages of gestation to within 42 days after the pregnancy has terminated. Risk factors include age greater than 35, unmarried status (owing to socioeconomic factors, including a lack of access to health care), and lack of prenatal care. The classic HIT triad (hemorrhage, infection, and toxemia or preelcampsia) contributes to about half of all maternal deaths. Approximately 300 women in the United States and 500,000 women in the world die every year from pregnancy-related causes. The maternal mortality ratio of 7.5 deaths per 100,000 live births in the United States did not changed significantly during the last 20 years of the twentieth century.

Preeclampsia. Preeclampsia, caused by high blood pressure during the latter part of pregnancy, is characterized by hypertension, protein in the urine, edema, and organ damage as a result of hypertension. Such organ damage may include seizure, stroke, kidney failure, liver damage, and fluid in the lungs. Preeclampsia is treated by effecting prompt delivery (and thereby ridding the body of the circulating toxin released by the placenta). Magnesium is commonly used to prevent seizure. Complications of severe preeclampsia can often be prevented with early diagnosis and appropriate treatment.

Obstetrical Hemorrhage. Obstetrical hemorrhage is characterized by excessive blood loss. It occurs prenatally as a result of premature separation (placental abruption) or abnormal location (placenta previa) of the placenta. It can also occur as a result of injury to the birth canal during delivery, retained placenta within the uterus after delivery, or the inability of the uterus to firm up (uterine atony) after delivery.

Puerperal Infection. Puerperal infections are those that occur during labor, delivery, or the postpartum period. The infection is typically caused by bacteria from the vagina ascending into the uterus. Risk factors include cesarean section, prolonged time from when the "water breaks" to delivery, poor nutrition, and maternal anemia. Prompt treatment with antibiotics can prevent significant morbidity associated with puerperal infections.

Embolism. An embolus is a clot. It could be a blood clot (thromboembolus), or a clot of fetal tissues (amniotic fluid embolus) that travels in maternal circulation. If it blocks off circulation in the lungs or the heart, the embolus could be fatal.

HEALTHY PREGNANCY

Between 1900 and 2000, infant mortality in the United States declined by 90 percent, and maternal mortality by 99 percent. This was one of the greatest achievements of public health in the twentieth century. However, the goal, established in 1994 by the International Conference on Population and Development, of every pregnancy being healthy has not been achieved. Current efforts to ensure healthy pregnancy work at three different levels of prevention.

Primary prevention involves efforts to prevent diseases from occurring during pregnancy. Examples of primary prevention during pregnancy include family planning, preconceptional care, and health promotion during prenatal care. By preventing unintended pregnancies, family planning can prevent morbidity associated with unintended pregnancies. Preconceptional care has been shown to reduce certain birth defects. Proper nutrition and cessation of tobacco, alcohol, and drug use during pregnancy can prevent low birth weight and other complications.

Secondary prevention involves efforts to facilitate early detection and treatment of diseases during pregnancy. Prenatal care provides early and continuous assessment of the pregnant woman, and includes early detection of preeclampsia, syphilis, and tuberculosis.

Tertiary prevention attempts to avert severe complications resulting from diseases during pregnancy. Examples of tertiary prevention include the administration of antibiotics in the treatment of puerperal infection, magnesium to prevent eclampsia (convulsions) in women affected by severe preeclampsia, and transfusion of blood products when obstetrical hemorrhage occurs. Regionalization of perinatal health services, so that high-risk women deliver only in hospitals equipped to deal with potential complications, plays an important role in tertiary prevention.

Much of the improvement in maternal and infant health is attributable to improved health conditions such as better sanitation, sewage control, and safer water supplies. Continued improvement is likely to come from social and behavioral changes rather than from advancement in medical care. Such developments as the expansion in the availability of legal abortions, increased education for women, and better family planning practices have all contributed to improved maternal and infant health. It is important, therefore, for public health professionals to learn how to better address social and behavioral determinants of health. For example, because smoking cigarettes during pregnancy can cause low birth weight and prematurity, it is important to find out how to stop women from smoking during pregnancy.

Because the health of a baby is tied to health of the mother, efforts to improve pregnancy outcomes must begin with women's health. Current efforts fall short by doing too little too late—to expect prenatal care to reverse all the cumulative effects of risk exposures over the course of a woman's life may be expecting too much. Future efforts should promote health not only during pregnancy, but during all of a woman's life.

MICHAEL C. LU

(SEE ALSO: Abortion; Abortion Laws; Birthrate; Child Health Services; Child Mortality; Contraception; Family Health; Family Planning Behavior; Fecundity and Fertility; Fetal Alcohol Syndrome; Fetal Death; Folic Acid; Infant Mortality Rate; Maternal and Child Health; Newborn Screening; Planned Parenthood; Prenatal Care; Reproduction; Women's Health)