Measurement of embryo volume at 7-10 weeks' gestation by 3D-sonography

The embryo volume (EV) is an important parameter for the early diagnosis of growth disorders. The objective of this study was to establish normal data for EV at 7-10 weeks' gestation with three-dimensional ultrasonography (3DUS). A cross-sectional study involving 50 pregnancies was performed. An endocavitary volumetric transducer (3D5-8EK) was used for all measurements. The VOCAL (Virtual Organ Computer-aided AnaLysis) method with a 30 degrees rotation angle was used for volumetric calculations. To analyse the correlation between EV and gestational age (GA) and crown-rump length (CRL), regression models were constructed. The mean, standard deviation, median, minimum and maximum values were calculated for each gestational age. The intraclass correlation coefficient (ICC) was used to determine inter- and intraobserver reliability. There was a significant correlation between EV and GA and CRL (R(2) = 0.951 and R(2) = 0.880, respectively). The exponential equation was the model that best expressed the correlation between these variables: [EV = exp(0.9481 x GA-8.117)] and [EV = 0.0871 exp(0.1207 x CRL)]. The mean EV ranged from 0.23 cm(3) (95% CI 0.03-0.42) at 7 weeks to 3.91 cm(3) (95% CI 3.85-3.96) at 10 weeks. Inter- and intraobserver correlation were excellent (ICC = 0.993 and 0.999, respectively). Embryo volume assessed through 3DUS increased from 7 to 10 weeks. Reference limits were generated for first trimester EV using 3DUS.