Fetal femur length, neonatal crown-heel length, and screening for intrauterine growth retardation.

Early ultrasonic diagnosis of intrauterine growth retardation (IUGR) can be very beneficial. However, most methods of ultrasonic diagnosis require an accurate knowledge of gestational age. The current study was designed to prospectively evaluate the relationship between fetal femur length and neonatal crown-heel length, and to study the femur length/abdominal circumference ratio as a method of screening for IUGR. Three hundred twenty-six infants who had undergone real-time ultrasound examination within 72 hours before birth were used for the study. Fetal femur length was compared with neonatal crown-heel length, although the most accurate relationship was geometric (r2 = .7474), and a strong linear relationship was also observed: y(crown-heel length) = 11.887 + 5.158 X (femur length), (r2 = .7067; SD = 3.34 cm). Mean femur length/abdominal circumference ratios were significantly different for average-for-gestational-age (22.33 +/- 1.86%), small-for-gestational-age (23.34 +/- 1.89%), and large-for-gestational-age (20.99 +/- 1.32%) infants, but did not reveal a discriminatory value for the diagnosis of IUGR as positive as that reported by Hadlock et al. The femur length/abdominal circumference ratio should be evaluated further as a screening tool in the diagnosis of IUGR.