Early transvaginal sonographic measurement of cephalic index

BACKGROUND: The aim of this study is to obtain normal values of cephalic index by transvaginal scan early in pregnancy. METHODS: In this prospective cross-sectional study, transvaginal high-resolution sonography was performed between 57 and 112 days' gestation in 1087 euploid fetuses. Measurements of cephalic index with standard deviations, calculated as the ratio biparietal diameter/occipito-frontal diameter, were obtained in the single gestational periods considered. RESULTS: Cephalic index was found to show fairly constant values throughout the period evaluated with smaller values of standard deviation. The best correlation with gestational age was described by a linear correlation. CONCLUSIONS: The data obtained by transvaginal scan can be used as parameters of normal values in early pregnancy.