Simplified method of determining fetal brain weight in utero.

Analysis of autopsy data shows that, from the 26th through the 38th gestational weeks, fetal brain weight (BrW) is a function of the 3.124 power of the largest head circumference (HC). Because there is excellent correlation between prenatal ultrasound measurement and postnatal tape measurement of the HC, it is possible to determine fetal BrW in utero. An alteration of the BrW:somatic weight (SW) relationship is an important physical stigma of asymmetric intrauterine growth retardation (IUGR). The value of longitudinal studies of fetal BrW and SW as a means of discriminating between normal and asymmetric growth is tested in a population at risk for IUGR.