Gestational sac volume by 3D-sonography at 7-10 weeks of pregnancy using the VOCAL method

Establish normative data for gestational sac volume (GSV) between 7 and 10 weeks gestation using three-dimensional ultrasonography (3DUS).

A cross-sectional study involving 74 normal pregnancies was performed to assess GSV between 7 and 10 weeks gestation. All measurements were performed using an endocavitary volumetric transducer. The virtual organ computer-aided analysis (VOCAL) method was used for volumetric calculations, with a 30 degrees rotation angle. To analyze the correlation between GSV and gestational age, regression models were constructed and adjustments were made using the determination coefficient (R (2)). For each week the mean, median, standard-deviation, minimum and maximum GSV values were calculated. The method proposed by Royston and Wright was used to calculate the reference intervals according to crown-rump length (CRL). The interclass correlation coefficient (ICC) and Bland-Altman graph were used to evaluate intraobserver variability.

There was a high correlation between GSV and gestational age (R (2) = 0.816). Mean GSV increased from 8.50 cm(3) at 7 weeks to 44.35 cm(3) at 10 weeks. There was also a significant correlation between GSV and CRL (R (2) = 0.693) with mean GSV increasing from 5.00 to 50.28 cm(3) for CRL between 9 and 40 mm. Intraobserver variability was excellent with an ICC = 0.9997 (95% CI, 0.9994-0.9998), with an average difference between measurements of 0.5 cm(3).

There is a correlation between GSV and CRL and this is a reproducible first trimester parameter. Reference limits for GSV using 3DUS were generated for pregnancies between 7 and 10 weeks.