The introduction of high resolution transvaginal US in obstetrical clinical practice permits earlier and more detailed visualization of embryo-fetal structures in early pregnancy. A transvaginal US examination with a high-resolution probe (5.0-6.0 MHz) was performed in 1246 pregnant patients between 9 and 16 weeks of gestation and known gestational age. Ten embryo-fetal biometric parameters were measured (crown-rump length, biparietal diameter, head circumference, transverse cerebellar diameter, thoracic circumference, mean abdominal diameter, abdominal circumference, femur length, humerus length and foot length). Reference ranges with 5 degrees and 95 degrees percentile intervals were constructed for all biometric parameters in relation to gestational age. Only one scan per patient was considered for this study. All the parameters evaluated demonstrated a high correlation with gestational age at polynomial regression analysis. The mean coefficient of determination (r2) ranged from 97.15 for biparietal diameter to 88.17 for transverse cerebellar diameter. The data are useful as reference range for the assessment of normal embryofetal development by transvaginal US in the early stages of pregnancy.