Prenatal ultrasound charts of orbital total axial length measurement (TAL): A valuable data for correct fetal eye malformation assessment

Objective: To construct prenatal age-specific reference intervals using ultrasound measurement of total axial length (TAL) in normal fetuses for assessing microphthalmia. Method: Prospective cross-sectional study of fetuses assessed at a prenatal ultrasound unit between 2011 and 2014. The study cohort comprised 309 pregnant women attending for routine fetal biometry, viability, or anomaly scan between 14 and 41weeks of gestation. Only singleton viable fetus with normal anatomy, adequate amniotic fluid, accurate gestational age, and no maternal medical complications of pregnancy were enrolled. Biometric measurements were obtained in the axial plane in all the fetuses. Those measurements and the relevant gestational age were registered in a computerized database. Results: A linear growth function was observed between gestational age and bi-orbital diameter (r²=0.95; p<0.001), ln (TAL) (r²=0.89; p<0.001), OD (r²=0.86; p<0.001), and IOD (r²=0.79; p<0.001). Tables showing the 5th, 50th, and 95th centiles of orbital parameters were created based on the reference interval charts. Conclusions: Ultrasound measurement of the fetal TAL ocular distance is feasible. This may assist the multidisciplinary team in the evaluation of fetal eye abnormalities that might be expressed by deviation in TAL.