Differences in sonographic measurements of the fetal head and chest

Differences in measurements using cephalometry and thoracometry ante partum are reported. Two examiners performed fetal head and thorax measurements shortly after one another using the same ultrasonic equipment without knowing the measurements achieved by each other. A series of 195 measurements were made by a few less experienced examiners. The values measured showed a considerable scatter. The average difference between the biparietal head measurements was 2.23 mm, and the standard deviation of the differences of the values measured was 1.94 mm. In a further group of 175 fetuses the measurements were performed by two skilled examiners. For the diameter of the head there was an average measured difference of 1.38 mm and a standard deviation of the differences of 1.11 mm. For the average thorax diameter--corresponding to the arithmetical average from the straight and transverse diameter--the following results were achieved. 4.14 mm average difference of value measured an 3.41 mm standard deviation in the measuring run performed by less experienced ultrasonic examiners as opposed to 2.57 mm average difference and 1.74 mm standard deviation in the group of practised examiners. The average thorax diameter showed a considerably smaller scatter than the transverse thorax measurement on its own. The differences in the values measured could not be seen to be dependent on the gestational age.