Biometry of early pregnancy with transvaginal sonography

A prospective cross-sectional study was performed in 248 pregnant women between 5 and 12 weeks' menstrual age with transvaginal sonography to establish biometric charts of the gestational sac, embryonic crown-rump length and biparietal diameter, amniotic sac and yolk sac to be used for assessment of gestational age and prediction of pregnancy failure. Polynomial regression analysis was applied and demonstrated a statistically significant positive correlation that could be described in all cases as a quadratic function, between gestational age and all the measurements with the exclusion of the yolk sac. Centile charts of both growth models and dating models were tabulated. The interrelationship between different measurements, including the gestational sac, crown-rump length, biparietal diameter and amniotic sac was also evaluated to produce age-independent charts. The dating model of the crown-rump length was found to have mean values similar to those described in transabdominal studies. The 95% reference interval was, however, 8.4 days, which was not lower than those reported in most transabdominal studies. It was concluded that transvaginal sonography was more able than the abdominal route to allow measurement of the crown-rump length in very early gestation, but did not yield a greater accuracy in predicting gestational age.