Intra- and interobserver repeatability of femur length measurement in early pregnancy.

Abstract

To assess the intra- and interobserver reproducibility of songographic measurement of fetal femur length between 10 and 16 weeks of gestation. Femur length was measured three times by the same trained observer in each fetus of 136 pregnant women. A second trained observer then repeated the measurements. The coefficient of variation, intraclass correlation coefficient and repeatability coefficient with 95% CIs were calculated for each observer and between the two observers. The inter- and intraobserver repeatabilities of femur length were good. For interobserver correlation, the coefficient of variation was 4.6% (95% CI, 3.0-6.2), the intraclass correlation coefficient was 0.82 (95% CI, 0.69-0.95) and the repeatability coefficient was 2.1 (95% CI, 1.8-2.7). For intraobserver correlation, the coefficient of variation was 4.2% (95% CI, 3.2-5.6), the intraclass correlation coefficient was 0.91 (95% CI, 0.75-0.97) and the repeatability coefficient was 3.23 (95% CI, 2.33-3.86) for Observer 2. Similar results were obtained for the other observer. Transvaginal femur length measurement is technically feasible and easy to perform between 10 and 16 weeks of gestation. The high degree of intra- and interobserver repeatability indicates it to be a reproducible method.