Optimal nutrition is integral to a healthy pregnancy, which can be described as “without physical or psychological pathology in mother or fetus, results in delivery of a healthy baby” (1
). Although the influence of poor nutritional status on adverse pregnancy outcome was documented early in the twentieth century, retrospective studies considering the effects of food shortages in the Netherlands during World War II clearly identified the influence of diet on pregnancy outcome (2
). Nutrition can affect the mother’s health and risk of pregnancy complications; it also affects the growth and development of the fetus, risk of birth defects, and health of the infant at delivery. Further studies have linked both undernutrition and overnutrition during pregnancy to increased risks of obesity, coronary heart disease, hypertension, diabetes, metabolic syndrome, and psychiatric disorders in the children; these findings suggest a persistent change in gene expression in response to the intrauterine environment (5
CURRENT PUBLIC HEALTH OBJECTIVES RELATED TO PREGNANCY AND NEONATAL HEALTH
Maternal and infant health are important predictors of the future health of the nation’s citizens. As identified in Healthy People 2020
, a major public health goal is to “improve the health and well-being of women, infants, children, and families” (9
). Public health issues related to maternal and child health include morbidity and mortality of pregnant and postpartum women; fetal, perinatal, and infant mortality; birth outcomes; prevention of birth defects; and access to preventive care. Progress has been made toward objectives related to fetal, infant, and maternal deaths; prenatal care; and prevention of neural tube defects (NTDs); however, the percentages of low birth weight (LBW) and preterm delivery have increased (10
). Healthy People 2020 objectives continue to emphasize the importance of nutrition, prenatal care, and preconception health in improving the health of mothers and infants (8
Nutritional status before pregnancy is a key factor in overall maternal health and in the risk of birth defects. Women who are contemplating pregnancy can make dietary and lifestyle changes that will reduce the risk of poor pregnancy outcome. The Centers for Disease Control and Prevention identified preconception risk factors for poor pregnancy outcomes (Table 52.1
) and developed 10 recommendations to improve preconception health (11
). Folic acid supplements before and during the early stages of pregnancy reduce the risk of NTDs and other birth defects. Ideally, all women of childbearing age should be consuming 400 µg/day of folic acid in addition to folate provide through foods (12
) because nearly one half of all pregnancies in the United States are unplanned (13
). Women following vegan or other strict vegetarian diets should also take supplemental vitamin B12 because the status of this vitamin is another risk factor for NTDs (12
Preconception iron status is important to reducing the risk during pregnancy of iron deficiency and anemia, which, in turn, can lead to intrauterine growth restriction (IUGR) and preterm birth (14
). Preconception care should include screening for iron deficiency anemia. Multivitamin and mineral supplementation may help to improve nutritional status in women who are following inappropriate diets, are avoiding numerous foods or groups of foods, are underweight, are trying to lose weight, or are abusing alcohol.
Achieving a healthy weight before pregnancy can improve chances of conception and pregnancy outcome and may improve lactation (13
). Women who are obese at the start of pregnancy are at greater risk of gestational diabetes mellitus (GDM) and preeclampsia and of experiencing induced labor and cesarean section. Obese women may also have more difficulty initiating breast-feeding (15
). Infants born to women who were obese before pregnancy are at increased risk of congenital abnormalities, NTDs, stillbirth, macrosomia, and obesity later in life (15
). Physical activity can help to improve weight and nutritional status; however, the amount of physical activity needed daily for weight management, chronic disease risk reduction, and enhanced physical fitness varies (18
TABLE 52.1 PRECONCEPTION RISK FACTORS FOR POOR PREGNANCY OUTCOME
Antiepileptic drug use
Folic acid deficiency
Hepatitis B infection
Human immunodeficiency infection/acquired
Oral anticoagulant use
Sexually transmitted diseases
From Johnson K, Posner SF, Biermann J et al. Recommendations to improve preconception health and health care: United States: a report of the CDC/ATSDR Preconception Care work group and the Select Panel on Preconception Care. MMWR Morb Mortal Wkly Rep 2006;55:1-23, with permission.
Management of preexisting chronic disease is another important element of preconception planning. Women with hypertension are at risk of maternal, fetal, and neonatal morbidity and mortality. The severity of hypertension and the presence of preeclampsia affect pregnancy outcomes (21
Diabetes increases the risk of birth defects, especially defects of the heart and central nervous system, and it also increases the risk of spontaneous abortion (21
). Attaining good blood glucose control before conception and during organogenesis can substantially reduce risks.
Approximately 3000 to 4000 women of childbearing age in the United States have phenylketonuria (PKU) without severe mental retardation (22
). To prevent mental retardation, microcephaly, and congenital heart disease in the infant, pregnant women with PKU must resume a low-protein, amino acid-modified diet during pregnancy (22
). Ideally, women with PKU should resume the diet before conception to regain control of blood phenylalanine and then maintain continued tight control throughout pregnancy.
MATERNAL PHYSIOLOGIC CHANGES DURING PREGNANCY
Numerous anatomic, biochemical, and physiologic changes occur during pregnancy to maintain a healthy environment for the growing fetus without compromising the mother’s health. Many of these changes begin in the early weeks of pregnancy, and together they regulate maternal metabolism, promote fetal growth, and prepare the mother for labor, birth, and lactation. A review of the physiologic changes during pregnancy sets the stage for understanding the changes in nutrient requirements that accompany pregnancy.
Maternal plasma volume begins to expand near the end of the first trimester, with a total increase in volume of 50% by 30 to 34 weeks of gestation. Red blood cell production is stimulated with a total increase in red blood cell mass of approximately 33%. Hematocrit levels decline until the end of the second trimester, by which time red blood cell synthesis is synchronized with plasma volume increase. Declining concentrations of plasma proteins and other nutrients are expected because of the expansion of blood volume. Poor plasma volume expansion predicts a poorly growing fetus and poor pregnancy outcome (23
Cardiac output increases approximately 30% to 50% during pregnancy. Elevated cardiac output occurs in response to increased tissue demands for oxygen and
is accompanied by an increase in stroke volume. The size of the heart increases by approximately 12%, probably because of the increased blood volume and cardiac output. Systemic blood pressure declines slightly during pregnancy, with the majority of the change occurring in diastolic pressure (5 to 10 mm Hg). Diastolic pressure returns to prepregnancy levels near term.
Respiratory changes support increased maternal and fetal requirements for oxygen. As the uterus enlarges, the diaphragm is elevated, which reduces lung capacity by about 5%, and residual volume is reduced by approximately 20%. Tidal volume increases as pregnancy progresses, resulting in increased alveolar ventilation and more efficient gas exchange, given that oxygen consumption increases only 15% to 20%. Respiration rate increases only slightly.
The kidneys increase slightly in both length and weight during pregnancy; and the ureters elongate, widen, and become more curved. Glomerular filtration rate increases by approximately 50%, and renal plasma flow rate increases by 25% to 50%. Renin levels increase early in the first trimester and continue to rise until term. Most pregnant women are resistant to the pressor effects of the resulting elevation of angiotensin II levels, but enhanced renin secretion may help to explain preeclampsia. A marked increase in excretion of glucose, amino acids, and water-soluble vitamins occurs, probably because the higher glomerular filtration rate presents higher levels of nutrients than the tubules can reabsorb.
Changes along the gastrointestinal tract support the increased demand for nutrients during pregnancy. Appetite increases, although initially this may be offset by nausea and vomiting. Motility of the gastrointestinal tract is reduced by increased levels of progesterone that, in turn, decrease the production of motilin, a hormone that stimulates smooth muscle in the gastrointestinal tract. Elongation in gastrointestinal transit time occurs largely in the third trimester of pregnancy and is not accompanied by a change in gastric emptying time (24
). Gallbladder emptying time is reduced and often incomplete.
The basal metabolic rate rises by the fourth month of gestation and is usually increased by 15% to 20% by term. An elevated basal metabolic rate reflects the increased demand for and consumption of oxygen. Most (50% to 70%) of the energy needs of the fetus are provided by glucose, with approximately 20% coming from amino acids and the remainder derived from fat. Use of fatty acids for fuel is enhanced in the mother to conserve glucose for use by the fetus.
TABLE 52.2 GESTATIONAL WEIGHT GAIN RECOMMENDATIONS
PREPREGNANCY BODY MASS INDEX (kg/m2)
TOTAL WEIGHT GAIN (kg)
RATE OF WEIGHT GAINa (MEAN; kg/wk)
a Second and third trimesters
Adapted with permission from Institute of Medicine, National Research Council. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: National Academies Press, 2009.