A Comparison of Crown‐rump Length Measurements Using a Real‐time Scanner in an Antenatal Clinic and a Conventional B‐scanner

In a series of 168 patients in the first trimester of pregnancy, fetal crown-rump length (CRL) measurements were attempted in the Antenatal Clinic using a linear-array real-time ultrasound scanner. The measurements could not be made in 23 of the patients; most of them had a gestational age of less than 10 weeks and the difficulty in obtaining measurements was usually due to an underfilled maternal bladder. When compared with CRL measurements obtained with a conventional B-scanner, a good correlation was obtained (r = 0.92); 80 per cent of the 'real-time' values fell within a range of +/- 5 mm of the conventional values. In all patients the estimates of gestational age using the two methods were within one week of each other.