Amniotic sac, fetal heart area, fetal curvature, and other morphometrics using first trimester vaginal ultrasonography and color Doppler imaging.

Ultrasonographic morphometric measurements were obtained with transvaginal ultrasonography from 121 patients with first trimester singleton pregnancies. Amniotic and gestational sac diameters, fetal heart area, and fetal length increased in a linear rate relative to crown-rump length, whereas the amniotic and gestational sac volumes increased at an exponential rate. The yolk sac exhibited a biphasic growth pattern with a peak at a crown-rump length of 3.5 cm. The ratio of crown-rump length to anteroposterior dimension increased over the first trimester, suggesting less curvature in older fetuses. In conclusion, vaginal ultrasonography permits accurate measurement of many new morphometric parameters.