Anthropometric equations for studying body fat in pregnant women

Anthropometric data from 200 pregnant women were used to estimate body fat at gestation weeks 14 and 37 and changes in body fat from week 14 to week 37 with four formulas from the literature. The resulting estimates were evaluated against the estimation of fat by a four-compartment model that determined fat from weight, total body water, bone mineral mass, and body density. The estimates of fat by existing anthropometric models were statistically different from those by the four-compartment model in both early and late pregnancy. Most importantly, the change in body fat estimated by the anthropometric models (all > 4 kg) was considerably higher than that estimated by the four-compartment model (3.3 kg). Two new anthropometric equations were developed, both of which used the four-compartment model as the reference method. The equation for predicting change in fat mass from week 14 to 37 of pregnancy was as follows: 0.77 (change in weight, kg) + 0.07 (change in thigh skinfold thickness, mm) - 6.13 (r² = 0.73). The equation for determining fat (kg) at term was as follows: 0.40 (weight at week 37, kg) + 0.16 (biceps skinfold thickness at week 37, mm) + 0.15 (thigh skinfold thickness at week 37, mm) - 0.09 (wrist circumference at week 37, mm) + 0.10 (prepregnancy weight, kg) - 6.56 (r² = 0.89). Both equations were derived on a randomly selected half of the total sample and validated on the remaining half. Both equations were found to be valid for use in studying pregnant women with different prepregnancy body mass indexes, different gestational weight gains, different ethnicities, and different socioeconomic status.