Ultrasound Nomograms of the Fetal Optic Nerve Sheath Diameter.

OBJECTIVE:  To construct prenatal age-specific reference intervals for sonographic measurements of the optic nerve sheath diameter (ONSD) during gestation in normal fetuses.

MATERIALS AND METHODS:  Prospective cross-sectional study of fetuses assessed in antenatal ultrasound units between 2010 and 2014. The examination was based on a technique for the sonographic assessment of ONSD previously published by our group. The mean values and SDs of the ONSD were modeled as a function of the gestational week by curve estimation analysis based on the highest adjusted R2 coefficient. Repeatability tests were performed to assess intraobserver variability and interobserver agreement.

RESULTS:  During the study period 364 healthy fetuses were enrolled. The mean values for the ONSD varied from 0.6 mm at 15-16 weeks to 2.8 mm at 37-38 weeks. The ONSD grows in a linear fashion throughout gestation, with a quadratic equation providing an optimal fit to the data (adjusted R2 = 0.957).

CONCLUSION:  Sonographic age-specific references for the fetal ONSD are presented. This data may assist in the decision-making process in fetuses with a suspected increase in intracranial pressure, or anomalies affecting the development of optic stalks, such as optic hypoplasia and septo-optic dysplasia.