Sonographic estimation of fetal age and weight.

Real-time ultrasound is a very effective tool in the estimation of fetal age and weight. The most accurate fetal age estimates are from crown-rump length measurements in early pregnancy. Late pregnancy age estimates are less accurate, but the use of multiple body measurements provides a composite age estimate generally accurate to within 7 per cent of actual age. Estimates of fetal weight are improved with the use of head, body, and femur measurements, and generally are accurate to within 15 per cent of actual birth weight.