Transvaginal volumetry of first trimester gestational sac:: A comparison of conventional with three-dimensional ultrasound

The aim of this study was to determine whether three-dimensional (3D) ultrasound is superior to two-dimensional (2D) ultrasound in evaluating first trimester gestational sac volume (GSV). 130 mainly low risk pregnancies between 5 and 12 weeks gestation were prospectively investigated. The 2D volumetry of GSV was performed using the ellipsoid formula; the 3D volumetry was carried out in all three planes using the contour mode and the volume from the measured circumferences and the distances between them were computed by a software. The data were analysed by variance and regression. The mean GSV increased from 1.5 +/- 2 mi with 5 weeks to 127 +/- 27 mi with 12 weeks (3D, longitudinal plane). The standard deviation of measured GSV increased with gestational age (GA) and GSV, and was more evident using 2D than 3D volumetry. GSV of pregnancies with similar GA differed considerably and viable pregnancies followed by miscarriage did not show different GSV. We conclude, that 3D volumetry of first trimester GSV is superior to 2D volumetry in its estimation, but seems to be without a prognostic significance for gestational outcome.