To assess the reliability of early biometric measurements in pregnancy, transvaginal sonography was performed in 92 pregnancies in the first trimester in a cross-sectional fashion. Measurements included crown-to-rump length (CRL), biparietal diameter (BPD), head and abdominal circumference (HC and AC), and femur length (FL). Stepwise regression analysis of the gestational age was performed. CRL maintained the highest correlation with gestational age (r = 0.99, p < 0.001). BPD, HC, AC also correlated well. FL showed a less strong correlation with gestational age (r = 0.76, p < 0.001). CRL remains the standard for early sonography measurements.