Ultrasonic measurement of femur length as a predictor of fetal gestational age.

Ultrasonic determination of fetal femur length is useful as a parameter in the determination of fetal gestational age. One hundred thirty measurements were made in pregnancies at 14 to 36 weeks' gestation. The measurements were plotted against gestational age, and we found that a strong correlation exists between fetal femur length and fetal gestational age, with 95% confidence limits of plus or minus seven days. This ultrasound parameter of fetal age assessment should be added to the other methods available for accurate dating of pregnancy.