New equations for estimating body fat mass in pregnancy from body density or total body water

The equations for estimating fat mass from body density or total body water are not appropriate for application in pregnancy, because the underlying assumptions with respect to density and composition of fat-free mass do not hold for pregnancy. Representative values have been derived from literature data for density and water content of maternal fat-free mass throughout pregnancy. Using these values we developed a method that provides new equations for estimating fat mass from body density or total body water for any desired stage of pregnancy. The validity of the new equations based on body density is discussed using data on body weight and body density obtained from a longitudinal study on well-nourished Dutch pregnant women. Because the new equations result in more valid estimates of maternal body fat mass, we suggest that they be used in studies on energy balance in pregnancy.