Nutrition During Pregnancy Part I: Weight Gain, Part II: Nutrient Supplements (1990) / Chapter Skim
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6 Body Composition Changes During Pregnancy
6 Body Composition Changes During Pregnancy
Pages 121-136
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From page 121... ...
Fetal growth may be influenced more by specific maternal tissue changes, for example, by accretion of lean tissue, fat, or body water, than by total gestational weight gain. Body composition studies in appropriate animals could provide valuable information in this regard.
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From page 122... ...
Therefore, a small relative error in the lean body mass estimation will produce a much larger relative error in calculated body fat. There are three standard methods for estimating lean body mass: measurement of total body water, determination of total body potassium content, and underwater weighing, which permits estimation of total body density, thereby allowing simultaneous estimation of both fat and lean tissue.
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From page 123... ...
Underwater Weighing Underwater weighing is based on the assumption that the weight of fat and lean tissue can be estimated from total body density by using standard values for the average densities of fat and lean tissues. Because of the increased hydration of lean tissue during pregnancy, and especially because added tissue includes little bone, which is dense, the density of the lean body mass is likely to decline during pregnancy.
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From page 124... ...
1b convert skinfold thickness measurements to estimates of body fat, standard regression equations are used. Generally, these are based on studies correlating skinfold thickness to body fat measured by total body water, body density, or total body potassium.
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From page 125... ...
Clearly, better understanding of the importance of lean tissue changes during pregnancy is needed. Development of this understanding will require further study of total body water, total body potassium, extracellular water, and plasma volume and their relationship to pregnancy outcome.
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From page 126... ...
Several newer methods (e.g., total body electrical conductivity, bioimpedance analysis, and computerized axial tomography) for measuring fat or lean tissue may produce accurate results quickly and relatively easily.
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From page 127... ...
The tabulated results illustrate the interpretive problems: wide variations in weight gains among studies (see Table 6-2) , different periods used to compute the gestational increment in body water, and small sample sizes.
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From page 128... ...
f The values for body water and pregnancy weight gain are the reported values from prepregnancy to 36 weeks of gestation. provide a means of evaluating the body water values obtained in the other studies.
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From page 129... ...
Nevertheless, the study by Forsum and colleagues is provocative, because it is the first longitudinal body water study that includes actual prepregnancy measurements. In addition, both the body water and total body potassium values they obtained suggest a loss of lean tissue in early pregnancy, as discussed below.
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From page 131... ...
from early to late pregnancy is approximately one-third that of the other two studies. The total body potassium data provided by Forsum's group, if correct, also suggest the loss of lean tissue during early pregnancy.
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From page 132... ...
Skinfold Thicknesses Skinfold thicknesses have been used to describe normal body fat changes throughout gestation, to determine whether skinfold thickness is associated with fetal outcome or with supplementation in undernourished women, to identify women with unusually small or large changes in body fat during pregnancy, and to estimate the initial body fat content. Measured mean triceps values range from a low of approximately 10 mm (at term in ~iwanese women; Adair et al., 1984)
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From page 133... ...
was used to compute body fat changes from skinfold thickness measurements. In light of the fact that the equation was derived from data on nonpregnant women, the general consistency of these findings with those from more complex methods is reassuring.
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From page 134... ...
Without these corrections, total body water tends to underestimate total body fat and both underwater weighing and total body potassium tend to overestimate it. · In the future, multicompartment models of body composition need to be used in studies of larger numbers of pregnant women.
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From page 135... ...
1974. Body fat assessed from total body density and its estimation from skinfold thickness: measurements on 481 men and women aged from 16 to 72 years.
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From page 136... ...
1988. New equations for estimating body fat mass in pregnancy from body density or total body water.
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