INTEROBSERVER VARIABILITY OF SONOGRAPHICALLY DETERMINED 2ND-TRIMESTERNUCHAL SKINFOLD THICKNESS MEASUREMENTS

Twenty physicians experienced in fetal sonographic evaluation obtained fetal nuchal skinfold thickness measurements in each of five pregnant women between 16 and 18 weeks' gestation. A random effects analysis o f variance model was used to explore the sources of variation in the s et of measurements, to determine the interobserver variability of sono graphically measured second-trimester nuchal skinfold thickness. It wa s possible to obtain 96 measurements. Four measurements (all in the sa me patient) were deemed unobtainable due to fetal position. All record ed measurements were between 1.7 and 4.5 mm. The means (and ranges) fo r the five patients were 2.7 (1.7-3.6), 2.9 (2.0-4.5), 2.7 (2.0-4.0), 3.3 (2.2-4.0), and 2.7 (1.8-4.0) mm. The standard deviation for intero bserver variability, caused by the combined effect of physician and ma chine imprecision, was 0.56 mm and the overall coefficient of variatio n was 19.8%. Interpatient differences were statistically significant ( p = 0.004). Interphysician differences were not (p = 0.11). We conclud e that experienced physician sonographers using high-resolution ultras ound equipment are able to obtain second-trimester muchal skinfold thi ckness measurements within 1.1 mm of the estimated true value with 95% probability.