A comparison of fetal biometric ratios to neonatal morphometrics.

Ratios of fetal abdominal circumference to femur length (AC/FL) and thigh circumference to femur length (TC/FL) have been suggested as indices of fetal nutrition. Birthweight, skin-fold thickness, and ponderal index are accepted neonatal indices of nutrition. The purpose of this study was to compare fetal to neonatal indices of nutrition. In 52 patients in term labor, fetal abdominal circumference, thigh circumference, and femur length were measured ultrasonographically. Neonatal skin-fold thickness was calculated as the average of tricipital, subscapular, abdominal, and anterior thigh measurements determined with Harpenden skin-fold calipers. Linear correlation analysis demonstrated a significant relationship between AC/FL and ponderal index (r = 0.340, P = 0.028) and between TC/FL and ponderal index (r = 0.368, P = 0.007). Neither AC/FL nor TC/FL were significantly related to birthweight or skin-fold thickness. These data suggest that the diagnostic reliability of antenatal studies of fetal biometric ratios may be enhanced by using the ponderal index as a neonatal endpoint rather than birthweight or skin-fold thickness.