Objective: Our purpose was to estimate, with the Cavalieri method of stereology and a point-counting technique, the volume of the fetus, fetal brain, fetal liver, and fetal lungs.
Study design: Four pregnancies were studied on three to five occasions at gestations from 27 weeks until term.
Results: In the four fetuses studied the total fetal volume increased at a rate of between 19.0 and 30.8 ml/day. The fetal liver constituted 2.5% to 4.9% of the total fetal volume; the fetal lung, 2.5% to 4.4%; and the fetal brain, 11.5% to 16.9%. The fetal liver increased in size by 0.4 to 1.3 ml/day; the lungs, by 1.2 to 1.4 ml/day; and the fetal brain, by 2.7 to 3.8 ml/day. The fetal brain/liver ratio, which may be an indicator of an asymmetric growth pattern, was between 2.4 and 5.6 with a tendency to a decreased ratio with increasing gestation.
Conclusion: This is the first serial study of total fetal volume and fetal organ volume with magnetic resonance imaging and stereology. Measurement of the total fetal volume and differential growth of fetal organs may be a more sensitive method of assessing fetal intrauterine growth than two-dimensional measurements obtained with ultrasonography.