van Raaij et al developed equations for predicting body fat mass during pregnancy. One set is based on total body water (TBW) while another is based on body density. The authors are from Agricultural University in De Dreijen, The Netherlands.
Patient selection: pregnant woman
Parameters:
(1) body mass in kilograms
(2) week of gestation
(3) total body water in kilograms
(4) presence or absence of generalized edema
fat mass in kilograms =
= (body mass) – ((total body water) / (factor))
Factor
No Edema or Leg Edema Only
Generalized Edema
10week gestation
0.725
0.725
20 week gestation
0.732
0.734
30 week gestation
0.740
0.748
40 week gestation
0.750
0.765
where:
• The factor usually is reported as 0.724. This is the water content of fat-free mass.
• As a pregnancy progresses the fat-free mass water content increases, resulting in a decline in the density of fat-free mass.
• Total body water may require special studies to determine such as deuterium-tracer studies.
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