Biparietal diameter and femur length discrepancies: are maternal characteristics important?

We examined whether gestational age, maternal race or height can be used to explain discrepancies between biparietal diameter- and femur length-derived gestational ages by analyzing ultrasound scans from 8041 consecutively scanned, singleton pregnancies, using multiple regression analysis. While a consistent association was noted between differences of more than 3 weeks and less than 3 weeks and advancing gestational age, neither maternal height nor race were significantly related. We conclude that, first, discrepancies between gestational age by biparietal diameter and femur length are rare (5%) and, second, the presence of discrepancies should not be dismissed on the basis of maternal stature or race and should alert the clinician to possible abnormal fetal growth or development.