Clinical utility of the relationship between fetal femur length and biparietal diameter.

The relationship between fetal femur length and biparietal diameter on ultrasound examination was evaluated in a large, unselected obstetric population of 12-40 weeks' gestational age. The derived ratio of fetal femur length to biparietal diameter was evaluated retrospectively as a tool for examining the technical reliability of fetal measurements obtained and as a screening mechanism for detecting asymmetric fetal development. The ratio of femur length to biparietal diameter is of value as an aid to the detection of fetal developmental anomalies and should be a routine parameter considered in the performance of an obstetric ultrasound examination.