Adequate Nutrition: A Key Element In Successful Childbearing
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Fetal development depends on genetic codes, maternal hormones, environmental factors and nutritional supplies. A nutritional deficiency or overdose at a critical time can contribute to poor development. Consuming sufficient protein and fluids, the inclusion of fresh fruits, vegetables, whole grains and beneficial fats, avoidance of alcohol, drugs, caffeine and tobacco, and a balance of energy expenditure in sports or recreation with periods of rest and recovery, are vital to success.
Adequate nutrition begins before conception. The B vitamins, folic acid, zinc, protein and omega-3 fatty acids are essential prior to conception and in the first trimester when hyperplasia is pronounced and initial organ development is underway. During gestation calories, protein and fluid intake are paramount. They affect cardiovascular parameters such as maternal blood volume and pressure, placental development and nutrient transport. Following birth, the mother’s recovery is dependent on the fuels available to repair tissue, nourish her organs and support breastfeeding.
Nutrition must be adequate to prevent low birth weight (LBW) and prematurity, as well as their sequellae of mental and physical disabilities. Babies born under 5.5 pounds (2500 grams) are considered LBW. Most LBW can be eliminated by improved prenatal nutrition–even small reductions in birth weight traced to reduced access to prenatal health care because of race or economic status [1]. Moderate aerobic exercise also reduces the risk for LBW [2] and maternal preeclampsia (pregnancy-induced hypertension with proteinurea), a gene-linked disorder is aggravated by low protein intake, lack of recreational exercise, and stress [3,4]. These two conditions have been on the rise in the U.S. recently. Technology is improving survival rates for these conditions, but prenatal care, nutrition and moderate exercise are keys to their prevention. Attention to these factors results in a healthy mother and — in the absence of genetic abnormalities, uncontrollable environmental factors or accidents — healthy mothers have healthy babies. Healthy babies born at full term are the goal.
What is Adequate Nutrition for a Childbearing Woman?
Proteins, carbohydrates, fats, vitamins, minerals and water are all necessary to achieve adequate nutrition in pregnancy. Extra calories are not required in the first trimester, according to the Institute of Medicine [1]. Height, weight, activity level and nutritional stress factors, plus about 300 extra calories/day in the 2nd trimester and about 500 extra in the 3rd trimester determine calorie requirements. Nutritional stress factors are nausea, vomiting and weight loss for a prolonged period, pregnancy spacing less than one year apart, prior poor obstetrical outcomes (stillbirths, spontaneous abortions, preterm deliveries), failure to gain adequate weight, age under 20 years, and emotional stress. For each stress factor add an additional 200 calories (400 extra calories maximum) [5, p. 607]. Calorie requirements will need to be refigured during pregnancy since very athletic women may become less active, there will be weight gain and/or loss, and there may be changing stress factors affecting the formula.
Macronutrients
Approximately 20–25% of calories in protein, 45–55% in carbohydrate and 30% in fat is an effective balance of macronutrients for insuring a steady level of blood sugar and nutrients. Consuming mini-meals of a few hundred calories every two to three hours is effective for clients who wish to avoid erratic energy states. Due to the metabolic preference to meet the fetal demand for energy and the tendency toward prenatal hyperinsulinemia, this strategy helps prevent blood sugar fluctuations.
Protein. Protein is needed for growth of the uterus, placenta and breast tissue, for production of amniotic fluid and a 40% or more increase in maternal blood volume, for storage reserves for labor, birth and breastfeeding, and to facilitate rapid fetal tissue growth. Adequate protein assists in magnesium retention, which reduces the risk for and/or severity of pregnancy-induced hypertension (PIH). Protein sources can contain complete or incomplete proteins; vegetarians must take care to include sufficient quanitities and efficient combinations of incomplete proteins.
Professional viewpoints vary as to how much protein is necessary in pregnancy. Kline recommends 0.8 gm protein per kg of body weight, plus 10 grams per day [6], in keeping with recommendations by the American College of Obstetricians and Gynecologists (ACOG) for an extra10 grams per day [7], and notes that women who are very active or under 14 years may require 1.0 gm of protein per kg of body weight. In this case, a 135 pound pregnant woman would require 60 to 70 grams of protein per day. However, there are other points of view [5, pp. 601–608], based on the fact that as much as 30% of protein intake may be stored during pregnancy and some broken down for fuel if total caloric intake is inadquate. Daily protein intakes of 25 to 30 grams per fetus beyond non-pregnancy levels are more likely needed [8]. This equates to 70 to 90 grams of protein per day for an average American woman with a singleton pregnancy. By adding 25 to 30 grams of protein per day to her needs based on weight and activity level, and taking in sufficient total calories (her other needs plus 300 calories per day), an athletic pregnant woman can be assured that she will provide adequate protein.
Carbohydrates. Complex carbohydrates and fiber foods such as fresh fruits, vegetables and whole grains are the most desirable immediate energy sources for pregnant women, as they also provide vitamins and minerals.For women without carbohydrate intolerance, simple and complex carbohydrates provide immediate, usable blood sugar. However, women with diabetes or gestational diabetes should follow the directions of their care provider.
Fats. Fetal fatty acids are provided solely by maternal supplies. Omega-3 fatty acids–alpha-lineolenic acid (ALNA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)–are important constituents of the prenatal diet. Insufficient levels of DHA are associated with impaired vision, nervous system disorders, low birth weight and premature delivery [9–11]. There is some evidence that during pregnancy maternal DHA levels fall and the potential for developing a deficiency increases [12]. Supplimentation of maternal intake of omega-3 fatty acids has been shown to increase fetal DHA levels [13]. By altering the omega-3 fatty acid content of cells through dietary changes, the risk of preeclampsia may be reduced. Williams found that women with the lowest levels of omega-3 fatty acids were 7.6 times more likely to have preeclampsia compared to those with the highest level [14]. Although fish are an excellent source of DHA and EPA (precursor of DHA), one needs to know where the fish comes from and whether there is any contamination associated with those waters, particularly mercury or lead. Omega-6 fats–available through nuts, seeds and vegetables, and their oils–aid the absorption of vitamins A, D, E, K and calcium, all of which are utilized in fetal development.
Micronutrients
Adequate levels of all vitamins and minerals are important in pregnancy. By eating a broad-based and colorful diet of whole foods, most of these micronutrients will be present. But, modern food consumption does not always allow for this. To prevent vitamin or mineral deficiencies women are asked by their care provider to take prenatal vitamins and/or minerals. To aid absorption, it is sometimes recommended that women take them on an empty stomach. However, this strategy can induce nausea and vomiting. These pills can be cut in small portions and taken with food throughout the day. Women taking iron pills who have constipation may be dehydrated. Dark stools indicate poor iron absorption; taking iron pills with vitamin C and fluids may help.
Vitamin A has been shown to have harmful effects when over-dosed. In one study, vitamin A intake above 10,000 IU daily resulted in birth defects of the head, heart, brain or spinal cord [15]. Vitamin B6 is helpful in preventing nausea and vomiting, and poor appetite. Women who avoid milk, eggs and fish should be considered for vitamin D supplimentation during pregnancy and lactation [16]. Vitamin K is necessary for production of prothrombin, which is required for blood clotting. Following delivery, women with vitamin K deficiencies, anemia or other clotting problems may hemorrhage, which is the primary cause of maternal mortality.
The greatest need for calcium comes in the third trimester. At 35 weeks, 330 mg/day is transferred from mother to fetus [17]. Low levels of both calcium and magnesium are associated with preeclampsia.The role of magnesium appears to be associated with its function as an activator of enzymes involved in membrane transport and integrity, and with its relationship to prostaglandins–specifically, the ratio of prostacyclins (vasodilators) and thromboxanes (some of which are vasoconstrictors), which is dramatically altered in the case of low serum magnesium. Both prostacyclin and thromboxane substances are increased during a normal pregnancy. However, women who develop preeclampsia have much smaller increases in prostacyclin production than other women, while thromboxane continues to rise at the same rate, thus increasing vasoconstriction and raising blood pressure.
Neonatal hypothyroidism is linked to maternal iodine deficiency. Some foods block iodine uptake when eaten raw in large amounts, including brussels sprouts, cabbage, cauliflower, kale, peaches, pears, spinach and turnips.While iron’s major function is binding oxygen to red blood cells (RBCs) for transport to oxygen-requiring sites, a phenomenon known as physiologic anemia can occur in pregnancy because plasma increases at a higher rate than RBCs. Iron deficiency can be due to low dietary intake or other causes, including internal bleeding, high phosphorous intake or prolonged antacid use. Sodium is vital to maintaining an adequate maternal blood volume. It is now well-established that pregnant women should salt to taste [18] and should not take diruretics. When severe edema occurs, the health care provider will look at blood pressure. Some edema is the natural consequence of the increased hormonal levels associated with pregnancy; however, severe edema is a classic symptom of preeclampsia.
Fluids
During pregnancy water does extra duty, helping to maintain an increased maternal blood volume, cooling both organisms (mother and fetus), and carrying off waste from increased metabolic functions. Eight 8-ounce glasses of water is the commonly accepted amount to be consumed daily. Athletic women need more and pregnant women living at high altitudes may need to consume twice this amount. While sports drinks may be useful for those with an intense or long duration work load, a snack consumed about an hour prior to exercise and water or watered-down 100% juice consumed during the workout may be preferable for the recreational exerciser.
The importance of water taken regularly during exercise cannot be over-emphasized. A few ounces consumed every ten or fifteen minutes during intense work is advisable. Athletes should drink water until their urine is clear. If women have questions about the safety of their tap water, they should contact their local health department or the Water Quality Association [19].
Conditions and Situations That May Affect Energy Balance
The value of adequate nutrition and an active pregnancy is evident in the results: a healthy, well-developed infant, and a healthy mother. Eating disorders, pregnancy-induced hypertension, anemia, or age-related factors can lead to adverse effects. Postnatal distress can be associated with body weight and shape concerns, disordered eating before and during pregnancy, and vomiting during pregnancy [20]. Low intensity exercise during early pregnancy can play a protective role. The most distressed mothers suffer from an eating disorder at the time of pregnancy. Binge and/or purge eating disorders are associated with more distress than a food restriction type of disorder.
Nausea and vomiting are fairly common in early pregnancy, but usually improve around the twelfth week. There are two major theories concerning normal nausea and vomiting in pregnancy. One regards the effects of altered hormone levels on the senses, emetic centers in the brain stem and gastric function, and on plasma glucose levels; and the other theory concerns allergic responses to possible environmental and food toxins [21–25]. Women in one research cohort with no symptoms of nausea or vomiting in early pregnancy showed a signficantly higher proportion of fetal death than among those with nausea or vomiting [26]. Such a finding gives impetus to the conventional wisdom that normal “morning sickness” is a sign of a healthy pregnancy. In practice, helping women through early pregnancy nausea and vomiting involves finding out which proteins they can eat and retain, to drink plenty of fluids and to maintain electrolyte balance. Sports drinks with 6 to 8% carboyhdrate can be helpful. Some women also find moderate exercise helpful. Eating plenty of protein and eating small quantities often can alleviate nausea caused by fluctuating blood sugar.
When vomiting continues and is severe, affecting electrolyte balance, nutritional status and weight gain, the term hyperemesis gravidarum applies. It is not always clear whether there is an underlying physical condition, and/or an associated behavioral problem. Even when a variety of pharmacological alterations have been tried, some women continue to be sick. Some non-pharmacological treatments have been found effective, including the use of powdered ginger [27], vitamin B6 [28], hypnotism [29], and accupressure [30].
Repeated ingestion of non-food substances during pregnancy is called pica. In the US, the most common items eaten are clay, corn starch, laundry starch, ice, dirt and baking soda. Women at greatest risk are black women living in a rural setting; white, urban women who ingest items such as ice, ashes and other substances, are known about, but less studied [31]. Culture and tradition appear to play a role, with family history being a risk factor. In one report of a rural midwest setting of 300 low-income postpartum women, 65% ate one or more pica substances during pregnancy [32]. Because non-nutrient items are substituted for food, pica interferes with a healthy nutritional status and can contribute to anemia, eclampsia and mineral deficiencies [31,33,34]. Awareness of pica by health and fitness professionals is a step toward locating and helping women with this disorder.
Alcohol, smoking and drugs have all been shown detrimental to the fetus. A woman wishing to have a healthy baby will avoid them. Fetal alcohol syndrome (FAS) can result in a variety of congenital malformations, growth restriction and neurological impairments. The organs affected by FAS develop early when a woman may not be aware she is pregnant, so avoiding alcohol for a period of time before conception is wise. Smoking is a major contributor to growth restriction and asthma in children. Drugs cross the placental barrier and are particularly dangerous to the fetal liver. All of these items interfere with nutrient utilization.
Hypertensive disorders in pregnancy are the most common medical complication. Pregnancy induced hypertension (PIH) is defined as elevated blood pressure after 20 weeks of gestation in women who did not have elevated blood pressure prior to pregnancy. In some women this may be an early sign of preecplampsia. Women with chronic hypertension prior to pregnancy or blood pressure at least 140/90 before 20 weeks gestation, are at increased risk for preeclampsia. The development of proteinuria, in addition to hypertension, is a sign of preeclampsia, and generally occurs after 20 weeks as well, although changes in the vascular system may occur by week 14, including increased peripheral vascular resistance, reduced cardiac output, reduced plasma volume, and decreased glomerular filtration rate with retention of salt and water [35]. As a result, there is reduced perfusion of the placenta and maternal kidneys, liver and brain. The fetus can suffer intrauterine growth restriction (IUGR) and even hypoxia. Altered fatty acid composition, in addition to vasospasm and other vascular symptoms, explain the hyperlipidemia, antioxidant deficiency, coagulation difficulties and ischemia or infarctions of the uterus and placenta that occur in preeclampsia [14,36]. At the end-stage of this disorder, eclampsia (also called toxemia), the mother can suffer convulsions, organ failure and death. Eclampsia is the third leading cause of maternal mortality [35].
Factors other than nutrition underly PIH and preeclampsia, but nutrition can be a factor in the severity of such disorders. There is an association of malnutrition, lower socioeconomic status and lack of education, as well as an association of stress and malnutrition, with increased risk of preeclampsia. Following a nutritional plan that includes adequate protein, particularly early in pregnancy, is one guideline usually given to women as a means of reducing the risk of developing severe hypertension. Especially women with a personal history or family history of hypertensive disorders need to take care to eat a healthy diet, include regular exercise in their routine and practice stress management.
Anemia includes physiologic anemia and pernicious anemias, such as cycle cell anemia or deficiencies in iron, B12 or folic acid, that affect the ability of red blood cells (RBCs) to adhere oxygen. Anemia is generally considered to be a hemoglobin level below 10 g/dL in the pregnant population [37]. If there is a serious hemoglobin pathology, exertion is likely to be contraindicated. On the other hand, if there is mild anemia that responds to iron taken in conjunction with Vitamin C, or to B12 or folic acid, it is not likely to require more than a temporary reduction of activities. It is important to note that hemoglobin levels in African-Americans are generally about 1 g/dL lower than those for whites, regardless of socioeconomic group [38]. Sickle cell disease occurs most frequently in African-Americans. Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency also occurs in African-Americans, as well as in those of Mediterranean descent [39].
It could be said that the ideal childbearing period of a woman’s life runs from the time she becomes physically mature (late teens to early twenties) to the time her lifestyle habits have dramatically affected her health status (mid-thirties). Childbearing before or after this period automatically places a pregnant woman in a high risk category. Before maturity, her nutritional intake must cover her own growth needs as well as those of her baby. As mid-life approaches, a woman may already have deficiencies that need to be assessed so that her dietary intake can minimize any detriment. For example, if her intake of calcium has been poor for many years, she will be at increased risk for osteoporosis if care is not taken to improve calcium intake.
How Adequate Nutrition Supports a Healthy Pregnancy
Building a healthy placenta, a strong uterus and a healthy baby, as well as protecting maternal nutitional stores, all rely on the mother’s dietary intake. Blood volume expansion makes adequate placental development possible. From a nutritional perspective, this means adequate protein and fluids to produce extra blood, as well as energy (calories) for the expression of hormones that direct placental development. Produced by the implantation of the embryo’s circulatory mechanism into the uterine circulation, the placenta is the locus of nutrient exchange between mother and fetus.
Oxygen, carbon dioxide, water, electrolytes and many vitamins and minerals are exchanged across the placental barrier–or membrane–by simple, or passive, diffusion. These substances flow from greater to lesser concentration. Nutrients in this category need to be present in sufficient quantities in the mother’s blood stream for simple diffusion to be effective. Glucose is transported by facilitated diffusion, as the fetus must have glucose for energy. It is aided in its transport across the placental barrier by its molecular configuration, even if maternal concentration is not much greater than fetal concentration. Without adequate energy, placental development is stunted, placing the baby at risk. Certain nutrients–amino acids, calcium, iron, potassium, phosphorus and vitamin B6–require active transport, an energy-requiring system. If these are not present in quantities that are adequate for both mother and baby, the fetus will use maternal stores, placing the mother at risk. If quantities are too low, both will suffer.
The uterus must grow from the size of a pear to that of a watermelon, and yet maintain the strength required for eight, twelve, or more hours of labor. To do this, the collagen that connects the multipennate muscle fibers of the uterus must stretch and the fibers themselves must maintain integrity. Protein, iron, zinc and vitamin C are particularly important with respect to these aspects of uterine development and activity.
Adequate maternal calorie and protein consumption are the primary concerns in assuring there is sufficient nutrition to create a healthy baby [39]. These are essential to prevent low birth weight, a small for gestational age (SGA) baby, pre-term delivery and a number of other conditions. Good nutrition–that is, nutrition containing adequate amounts of a range of nutrients–is essential to produce optimal brain and organ development, as well as important functions such as storage of iron in the fetal liver.
The effects of poor nutrition in the first trimester include poor fetal development, a lighter and smaller placenta, prematurity and low birth weight, lower Apgar scores and maternal anemia. During the second and third trimester, poor nutrition has a negative effect on the baby’s growth, including development of the nervous system, and contributes to pregnancy-induced hypertension (PIH). The state of maternal nutrition in the months leading up to pregnancy also plays a role in fetal development, such as the need for adequate folic acid [40]. A deficiency can result in impaired cell division, megaloblastic anemia, and a number of sequellae including fetal malformation (including neural tube defects), spontaneous abortion, eclampsia, pre-term delivery, SGA and prenatal hemorrhage [9].
The fetus places substantial demands on the mother’s body during pregnancy. The liver must produce albumin, the osmotic substance that draws fluid from cells into the blood stream in order to produce the large blood volume required to sustain a placenta and fetus. The kidneys work to filter the additional blood volume. The brain and glands produce high levels of reproductive hormones. Raw materials are needed for the array of metabolic functions required in pregnancy, and adequate nutrition protects maternal health by protecting her energy resources.
Maternal Weight Gain
Maternal weight gain has traditionally been used to evaluate the state of a pregnancy. As of 2009, the National Academy of Science [1] recommends that pregnancy weight gain be based on a woman’s pre-pregnancy BMI. The National Heart, Lung and Blood Institute provides a BMI calculator here: http://www.nhlbisupport.com/bmi/. A pre-pregnancy BMI less than 18.5 (low) should have a total weight gain of 28 to 40 pounds (12.7 to 18 kg); BMI between 18.5–24.9 (normal) should gain 25 to 35 pounds (11.3 to 16 kg); and those BMI 25.0 to 29.9 (high) should gain 15 to 25 (6.8 to 11.3 kg) pounds. Weight gain for obese women (BMI over 30.0) should be limited to 11 pounds.
First trimester weight gain usually rises at a slower pace than second or third trimester gain and may be negatively influenced by nausea and vomiting. When dietary intake is based on adequate calories and protein, weight gain should be in the correct range for an individual woman, unless there is an underlying medical condition. Ultrasound imaging is now used by health care providers as much as weight gain or fundal height (the measurement from pubic bone to top of the uterus) to determine if fetal growth is progressing at a satisfactory rate.
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References
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