Hytten and Leich reported an equation for predicting the total body water (TBW) for a fetus based on body weight.
Patient selection: normal fetus
(1) body weight in kilograms
percent body weight =
= (0.7936 * ((weight)^2)) – (8.1011 * (weight)) + 90.3094
• The TBW for a fetus with hydrops fetalis would not be adequately estimated by this equation.
If the gestational age is used (assuming normal fetal development):
TBW in mL per kg body weight =
10 to 113 days
= 926 + (0.00512 * (gestational age in days)) - (0.002024 * ((gestational age in days)^2))
113 to 250 days
= 1006 - (0.9402 * (gestational age in days))
from Figure 12.1 Hytten and Leitch
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