The aim of our study was to assess the volume of the gestational sac and yolk sac throughout the first trimester of pregnancy, and to establish the relationship between the yolk sac volume measurements and vascularity visualization rates. Eighty women with uncomplicated singleton pregnancies between 5 and 12 weeks were evaluated by three-dimensional and color Doppler ultrasound (Combison 530, Kretztechnik). Regression analysis revealed exponential rise of the gestational sac volume with gestational age throughout the first trimester. An exponential rise of the yolk sac volume was noticed between gestational weeks 5 and 8, followed by gradual increase of the yolk sac volume between the gestational weeks 8 and 10. After reaching the plateau from 10 to 11 weeks, yolk sac volume started to decrease. The highest visualization rates for the yolk sac vessels were obtained between gestational weeks 7 and 8. When yolk sac reached the maximum size between 10 and 11 weeks, reduced vascularity was demonstrated. Three-dimensional ultrasound allowed estimation of the gestational sac and yolk sac volumes throughout the first trimester of pregnancy. Both of these measurements seem to be useful prognostic parameters for the pregnancy outcome. The combination of functional and volumetric data provides much useful information on early human development.

The aim of the study was to correlate intra-observer reproducibility of the nuchal translucency measurements by two-dimensional and three-dimensional transvaginal ultrasound. Examinations were performed on 120 women undergoing ultrasound screening at 10 to 14 weeks' gestation. They were examined by two experienced ultrasonographers using both methods two times consecutively. Statistical analysis for the assessment of intra-observer reproducibility was paired t-test. Nuchal translucency measurements were obtained in 100% of cases with three-dimensional sonography compared to only 85% with two-dimensional sonography. Better intra-observer reproducibility was obtained for three-dimensional than for two-dimensional ultrasound. Three-dimensional transvaginal ultrasound improves accuracy of nuchal translucency measurement allowing appropriate mid-sagittal section of the fetus and clear distinction of the nuchal region from the amniotic membrane.