Reference range of embryo volume by 3-D sonography using the XI VOCAL method at 7 to 10 + 6 weeks of pregnancy.

We sought to establish normative data for three-dimensional ultrasound (3DUS) first-trimester embryonic volume using the extended imaging virtual organ computer-aided analysis (XI VOCAL) technique. This cross-sectional study involved 64 normal pregnancies at 7 to 10 + 6 weeks' gestation. Embryonic volume was obtained on 3DUS using the XI VOCAL technique with manual outline of 10 sequential planes. The mean, median, standard deviation, and maximum and minimum values were obtained for each week calculated. Polynomial regression models adjusted by the determination coefficient (R(2)) were created to assess the correlation between embryonic volume and gestational age (GA) and crown rump length (CRL). The intraclass correlation coefficient (ICC) was used to calculate inter- and intraobserver reproducibility. Mean embryonic volume went from 0.20 cm(3) (range 0.10 to 0.89 cm(3)) to 5.12 cm(3) (range 2.90 to 5.98 cm(3)). Embryonic volume was strongly correlated with GA (R(2) = 0.84) and with CRL (R(2) = 0.87). There was a good inter- and intraobserver reproducibility of embryonic volume with ICC = 0.999 and 0.995, respectively. Reference range for 3DUS first-trimester embryonic volume using the XI VOCAL technique were generated for pregnancies at 7 to 10 + 6 weeks, with high inter- and intraobserver reproducibility.