Early transvaginal measurement of cephalic index for the detection of Downsyndrome fetuses

Objective: The aim of this study was to produce normal cephalic index value s by transvaginal scan early in pregnancy and to evaluate the screening uti lity of this measurement for the identification of fetuses at risk for Down syndrome. Method: In this prospective cross-sectional study, transvaginal high-resolution sonography was performed between 9 and 16 weeks of gestatio n in 1,087 euploid fetuses and 36 Down syndrome fetuses. Measurements of th e cephalic index, calculated as the ratio biparietal diameter/occipito-fron tal diameter, were plotted against gestational age. Results: The cephalic i ndex was found to show fairly constant values throughout the period evaluat ed. The best correlation with gestational age was described by a linear cor relation, All the measurements obtained in Down syndrome fetuses were withi n the normal ranges. Conclusion: Our data show that in early pregnancy the cephalic index cannot be considered a useful tool in the detection of fetus es at risk for Down syndrome.