ABSTRACT
OBJECTIVE: The purpose of this study was to establish reference ranges for the fetal orbital diameters (OD) and outer orbital diameters at 16 to 38 weeks' gestation. METHODS: This prospective longitudinal study enrolled 41 consecutive women with uncomplicated singleton gestations during their first trimester of pregnancy. Serial measurements of the fetal orbits by ultrasound examination were performed at intervals of 4 weeks until 28 weeks, and then every 2 weeks until 36 weeks, and weekly thereafter. Linear regression was used for statistical analysis. RESULTS: A total of 331 fetal orbital diameters and 298 outer orbital diameters were measured. The reference ranges for orbital diameters and outer orbital diameters were presented as mean, 95% confidence interval of the mean and percentiles. A linear growth function was observed between gestational age (GA), orbital diameter (Y=0.654 x GA - 0.856; r2=0.948; p<0.0001) and outer orbital diameter (Y=1.679 x GA+0.510; r2=0.942; p<0.0001). Significant correlation was also found between orbital diameter and outer orbital diameter (Y=2.451 x OD+4.840; r2=0.906; p<0.0001). CONCLUSION: We have presented percentile tables and regression formulas for fetal orbital diameters and outer orbital diameters. These results provide normative data of the growth of the fetal orbit and may be useful in assessing fetal orbital architecture in patients at risk of ocular abnormalities.