Three fetal ponderal indexes in normal pregnancy

The relationship of three different fetal ponderal indexes was studied in 116 normal pregnancies between 20 and 41 weeks. All three fetal ponderal indexes were found to be independent of gestational age. Throughout normal gestation, the femur length to abdominal circumference ratio X 100 was found to be 22.3 +/- 2.4 (mean +/- 2 SD), the tibia length to abdominal circumference ratio X 100 19.3 +/- 2.2 (mean +/- 2 SD), and the femur plus tibia length to abdominal circumference ratio X 100 41.6 +/- 4.2 (mean +/- 2 SD). The clinical applications of the different fetal ponderal indexes in evaluating fetal growth are discussed. Because they are independent of gestational age, the fetal ponderal indexes should prove most useful in evaluating fetal growth in high-risk patients with unknown dates.