Crown rump length: a comparison of real time scanning and conventional compound scanning. The interindividual measuring variation between two operators

Ultrasonic measurements of crown rump length (CRL) obtained by conventional compound scanning and real time scanning were compared. Normal growth curves for fetal CRL were determined for both types of equipments. The curve for mean values found on the real time scanner ran parallel to and above the mean values found on the compound scanner because of a systematic underestimation by one operator on the latter scanner.A comparison of the interindividual measuring variation was done in 39 patients where both authors independently on the same day measured CRL on the same patient using both equipments. The conclusion drawn is that the real time scanner offers an advantage over conventional compound scanner by facilitating location of the fetal long axis and improving reproducibility of measurements, particularly in the hands of an inexperienced operator.