Intra‐ and interobserver repeatability of femur length measurement in early pregnancy

OBJECTIVE: To assess the intra- and interobserver reproducibility of songographic measurement of fetal femur length between 10 and 16 weeks of gestation. METHODS: 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. RESULTS: 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. CONCLUSION: 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.