“Any obstetrician who allows a woman to lose her attrac-tiveness (i.e., gain too much weight) is depriving her of many
things that make for her mental well-being, her husband’s contentment, and her own personal satisfaction.”
Loughran, American Journal of Obstetrics and Gynecology, 1946
Weight gain during pregnancy is an important considera-tion because newborn weight and health status tend to increase as weight gain increases. Birth weights of infants born to women with weight gains of 15 pounds (7 kg) for example, average 3100 grams (6 lb 14 oz). This weight is about 500 grams less than the average birth weight of 3600 grams (8 lb) in women gaining 30 pounds (13.6 kg).
Rates of low birth weight are higher in women gaining too little weight during pregnancy.26 Weight gain during pregnancy is an indicator of plasma volume expansion and positive calorie balance, and provides a rough index of dietary adequacy.73
Multiple studies show broad agreement on amounts of weight gain that are related to the birth of infants with weights that place them within the lowest category of risk for death or health problems.34 Yet how much weight should be gained during pregnancy remains a hotly debated topic. Earlier in the last century, when gains were routinely restricted to 15 or 20 pounds, weight gain in pregnancy was seen as the cause of pregnancy hypertension, difficult de-liveries, and obesity in women. Pregnant women would be placed on low-calorie diets and given diuretics and amphet-amines and urged to use saccharin to limit weight gain.74
Although none of these notions have been shown to be true, weight gain during pregnancy still represents a prickly issue. Weight gain and body weight are not only a matter of health, but are also closely linked to some peo-ple’s view of what is socially acceptable.
Psychological and sociological biases related to body weight and shape in women are an important reason to apply recommendations for weight gain in pregnancy based on scientific studies and consensus.
Pregnancy Weight Gain Recommendations
Current recommendations for weight gain in pregnancy are based primarily on gains associated with the birth of healthy-sized newborns (approximately 3500–4500 g or 7 lb 13 oz to 10 lb).33 As shown in Illustration 4.10, how-ever, prepregnancy weight status influences the relation-ship between weight gain and birth weight. The higher the weight before pregnancy, the lower the weight gain needed to produce healthy-sized infants. Recommended weight gains for women of all ethnicities and statures entering pregnancy underweight, normal-weight, overweight, and obese are displayed in Table 4.17.75 This table also presents the range in weight gain provisionally recommended for twin pregnancy.75 (Weight gain recommendations for twin pregnancy are presented in more detail in Chapter 5.) This change represents an adaptation by the body to
how glucose utilization is programmed to operate.
What adaptations are made to ensure the CNS gets priority access to glucose? Animal studies indicate that the expression of genes that produce insulin receptors on muscle cell membranes may be suppressed in response to a low availability of glucose. This increases insulin resist-ance and decreases uptake of glucose by muscle cells, and reduces their growth. It also increases the availability of glucose for CNS development.
Adaptations that decrease muscle utilization of glu-cose and reduce muscle size may serve the offspring well later in life if food availability and intake are limited. If food is abundant and food intake is high, however, such adaptations may lead to elevated blood levels of glucose and insulin. These changes may increase the risk of obesity, type 2 diabetes, gestational diabetes, and other disorders associated with insulin resistance.69
Increased susceptibility to insulin resistance and weight gain in infants experiencing nutritional insults in utero has been attributed to a “thrifty phenotype,” or ge-netic functional types programmed in utero that act to conserve energy.70
The function of genes involved in cholesterol metab-olism appear to be modified in males with birth weights less than 3.2 kg (7 lb). In these individuals, production of “good” cholesterol, HDL, tends to decrease in re-sponse to high-fat, high-saturated-fat diets. HDL choles-terol production generally increases in males with higher birth weights in response to this type of diet. High blood levels of HDL-cholesterol are protective against heart disease.71
Some studies have shown a link between maternal nu-tritional exposures during pregnancy and later disease risk in infants with a wide range of birth weights. Low weight gain around mid-pregnancy, for example, has been associ-ated with higher blood pressure in children, and low levels of maternal body fat during pregnancy with increased risk of heart disease in offspring.72
Limitations of the Fetal-Origins Hypothesis
The hypothesis that maternal and fetal nutritional expo-sures influence later disease risk is gaining support and recognition. Many questions are unanswered, however.
Which specific nutritional exposures are responsible for changes in gene function and increased disease risk? When do the vulnerable periods of fetal sensitivity to poor nutri-tion occur? What levels of energy and nutrient availability are related to the optimal functioning of genes? How can we “rescue” or repair detrimental epigenetic changes so that they correspond to a person’s actual rather than in utero or early-life exposures? Progress is being made to-ward finding out answers to each of these questions. The implications of the associations between maternal and fe-tal nutrition and adult disease risk are immense.
33411_04_Ch04_p087-133.indd 104
33411_04_Ch04_p087-133.indd 104 4/30/10 3:40:24 PM4/30/10 3:40:24 PM
Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.
Restriction of pregnancy weight gain to levels below the recommended ranges is not recommended. It does not decrease the risk of pregnancy- related hyperten-sion and is associated with increased infant death and low birth weight, and poorer
offspring growth and development.20 In addition, low weight gain in pregnancy may increase the risk that infants will develop heart disease, type 2 diabetes, hypertension, and other types of chronic disease later in life.35
Rate of Pregnancy Weight Gain Rates at which weight is gained during pregnancy appear to be as im-portant to newborn outcomes as is total weight gain.
Low rates of gain in the first trimester of pregnancy may down-regulate fetal growth and result in reduced birth weight and thinness.78 For underweight and normal-weight women, rates of gain of less than 0.5 pound (0.25 kg) per week in the second half of pregnancy, and of less than 0.75 pound (0.37 kg) per week in the third trimester of pregnancy, double the risk of preterm delivery and SGA newborns. For overweight and obese women, rates of gain of less than 0.5 pound (0.25 kg) per week in the third trimester also double the risk of preterm birth.79 Third-trimester weight gains exceeding approxi-mately 1.5 pounds a week (0.7 kg), however, add little to birth weight in normal-weight and heavier women, and may increase postpartum weight retention.80
Rate of weight gain is generally highest around mid-pregnancy—which is prior to the time the fetus gains most of its weight (Illustration 4.11). In general, the pattern of gain should be within a few pounds of that represented by the weight-gain curves shown in Illustration 4.12.34 Because underweight women tend to retain some of
the weight gained in pregnancy for their own needs, they need to gain more weight in pregnancy than do other women. Overweight and obese women, on the other hand, are able to use a portion of their energy stores to support fetal growth, so they need to gain less.
Duration of gestation, smoking, maternal health status, gravida, and parity also influence birth weight. Consequently, gaining a certain amount of weight during pregnancy does not guarantee that newborns will be a healthy size. It does improve the chances that this will happen, however.
Approximately 40% of U.S. women gain within the recommended weight ranges during pregnancy.76 For all except the obese, women who gain within the recom-mended ranges are approximately half as likely to deliver low-birth-weight or SGA newborns as are women who gain less. Rates of LGA newborns, Caesarean-section de-liveries, and postpartum weight retention tend to be higher when pregnancy weight gain exceeds that recommended.76 It is suggested that insulin resistance may be related to ex-cessive weight gains during pregnancy and some of the adverse neonatal outcomes.77
Table 4.17 Pregnancy weight gain recommendations75
Prepregnancy Weight Status Body Mass Index
Recommended Weight Gain Underweight, ,18.5 kg/m2 28–40 lb (12.7–18.2 kg) Normal weight,
18.5–24.9 kg/m2 25–35 lb (11.4–15.9 kg) Overweight,
25–29.9 kg/m2 15–25 lb (6.8–11.4 kg) Obese, 30 kg/m2 or higher 11–20 lb (5.0–9.1 kg) Twin pregnancy 25–54 lb (11.4–24.5 kg)
Gravida Number of pregnancies a woman has experienced.
Parity The number of previous deliveries experienced by a woman; nulliparous 5 no previous deliveries, primiparous 5 one previous delivery, multiparous 5 two or more previous deliveries. Women who have delivered infants are considered to be “parous.”
3800
3600
3400
3200
3000
2800
Birth Weight (g)
Weight Gain (lb)
0 10 20 30 40 50
Pregnancy Weight Status
Very Obese Obese Over Normal Under
Illustration 4.10 Pregnancy weight gain by prepregnancy weight status and birth weight.
source: From Clinical Nutrition, Vol. 7, Fig. 1, p. 186, J. E. Brown, © 1988.
Reprinted by permission from Elsevier.
12
kg 28
4 8 12 16 20 24 lb
3 kg
1 2
2 4 6 8 10
Weeks of Pregnancy
Maternal Weight Gain Fetal Weight
40
8 12 16 20 24 28 32 36
Pregnancy weight gain
Fetal weight gain
Illustration 4.11 Rates of maternal and fetal weight gain during pregnancy.
source: Curves drawn by Judith E. Brown, 2002.78
33411_04_Ch04_p087-133.indd 105
33411_04_Ch04_p087-133.indd 105 4/30/10 3:40:25 PM4/30/10 3:40:25 PM
Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.
33411_04_Ch04_p087-133.indd 106
33411_04_Ch04_p087-133.indd 106 4/30/10 3:40:25 PM4/30/10 3:40:25 PM
Copyright 2011 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.
Text not available due to copyright restrictions
Some weight (3 to 5 pounds) should be gained in the first trimester, followed by gradual and consistent gains thereaf-ter. The rate of weight gain often slows a bit a few weeks prior to delivery, but as is the case for the rest of pregnancy, weight should not be lost until after delivery.78
Composition of Weight Gain in Pregnancy
A question often asked by pregnant women is, “Where does the weight gain go?” Where the weight gain gener-ally goes by time in pregnancy is shown in Table 4.18.
The fetus actually comprises only about a third of the to-tal weight gained during pregnancy in women who enter pregnancy at normal weight or underweight. Most of the rest of the weight is accounted for by the increased weight of maternal tissues.
Body Fat Changes Pregnant women store a significant amount of body fat in normal pregnancy in order to meet their own and the fetus’s energy needs, and quite likely to prepare for the energy demands of lactation. Body fat stores increase the most between 10 and 20 weeks of pregnancy, or before fetal energy requirements are high-est. Levels of stored fat tend to decrease before the end of pregnancy. Only 0.5 kg of the approximately 3.5 kg of fat stored during pregnancy is deposited in the fetus.12,30
Postpartum Weight Retention
Concern about the role of pregnancy weight gain in foster-ing long-term maternal obesity has increased in the United States, along with the rising incidence of obesity in adults.
Increased weight after pregnancy appears to be related to a variety of factors, including excessively high weight gain in pregnancy (over 45 lb, or 20.5 kg), weight gain after delivery, and low activity levels.81 High blood levels of in-sulin early in pregnancy, and levels of leptin, have been related to increased weight gain during pregnancy. Levels of both hormones are related to diet.82,83
Women tend to lose about 15 pounds the day of deliv-ery, but subsequent weight loss is highly variable.81 On av-erage, however, women who gain within the recommended ranges of weight gain are 2.0 pounds (0.9 kg) heavier 1 year after delivery than they were before pregnancy.84 This gain is slightly above the amount of weight women tend to gain with age.85 Postpartum weight retention tends to be slightly less in women who breastfeed for at least 6 months after pregnancy.86 Women who gain less than the recommended amount of weight gain in pregnancy do not retain less weight on average after pregnancy than do women who gain within the ranges.89 Postpartum weight can be reduced by identifying high weight gainers during pregnancy and getting the women identified involved in an exercise and healthy-eating program.87