Reference values of fetal orbital measurements by transvaginal scan in early pregnancy

OBJECTIVE: To construct reference ranges of orbital diameters, measured in early pregnancy by transvaginal sonography. METHODS: The study group consisted of 2717 fetuses of pregnant women referred to our center and examined by transvaginal ultrasound between 11-16 week's gestation. Nomograms with confidence intervals (5th and 95th percentile) for each orbital measurement (orbital diameter, interocular and binocular distance) versus gestational age were produced. RESULTS: The orbital measurements increased in a linear fashion throughout early pregnancy with a good correlation with gestational age. CONCLUSION: Transvaginal sonography is able to visualize and measure orbital diameters with accuracy in early pregnancy; reference ranges were developed that can be used to evaluate normal orbital development and can be helpful in the detection of syndromes with orbital growth defects and other associated fetal anomalies.