Introduction: We investigated the correlation of amniotic fluid (AF) concentrations of glial fibrillary acidic protein (GFAP) with prenatal features of myelomeningocele (MMC) and neurodevelopmental outcome after fetal MMC (fMMC) surgery.Materials and Methods: AF was collected during fMMC surgery between December 2012 and November 2015. AF-GFAP concentration was determined by ELISA. Retrospective chart review identified the characteristics of the defect. Data regarding delivery and 1-year neurodevelopmental outcome was collected from The Children's Hospital of Philadelphia fMMC Registry.Results: Eighty-two AF samples were collected from fMMC surgeries. Perinatal data were obtained from 77 subjects, and 1-year follow-up data from 65 subjects. GFAP concentrations were significantly elevated in MMC compared to myeloschisis (24.1 ± 2.9 and 10.3 ± 1.5 ng/mL; p < 0.0001). A larger percentage of subjects with myeloschisis defects delivered before their scheduled due date (myeloschisis 88.5%; MMC 55.0%; p = 0.003) and delivered at an earlier mean gestational age (34.6 ± 0.4 weeks, n = 26) compared to those with MMC defects (35.2 ± 0.4 weeks, n = 51) (p = 0.04).Discussion: AF-GFAP levels differentiate between MMC and myeloschisis, and raise interesting questions regarding the clinical significance between the 2 types of defects. [ABSTRACT FROM AUTHOR]