Lower extremity movement (LEM) in fetuses undergoing prenatal myelomeningocele (MMC) repair is generally assessed at a neonatal evaluation (NE). Ultrasound (US) can assess LEM antenatally, but the correlation between US and NE is not firmly established, nor have differences in US findings on different postoperative days (POD) been correlated with NE. This was a retrospective cohort correlation study of fetuses that underwent open repair of myelomeningocele at SSM Cardinal Glennon Fetal Care Institute, St. Louis MO between January 2011 and December 2016. Movement of the lower extremities at the toe, ankle, knee, and hip of each leg was assessed by US at the initial visit, after open repair on POD 0-5, and at 32 weeks gestation. After delivery, NE was performed by physical therapists and a neurosurgeon, with 94% occurring in the first month of life. 41 fetuses were included. Follow-up was 100%. Movement at the ankle at the initial visit was associated with the function in the same joint on NE. US of the ankle and knee on POD 3 were strongly predictive (k=0.710, 0.420-1.000 and k= 0.577, 0.152-1.000, respectively). Ankle US on POD 4 was also strongly correlated with NE of the ankle (k=0.659, 0.308-1.000). Any LEM varied by POD: it was present on POD 1 in 45.2% of fetuses who showed neonatal movement and increased to 100% by POD 5. Postoperative US assessment of movement in the knee, ankle, and toe in fetuses undergoing open fetal MMC repair correlates with NE. POD 3 assessments at the ankles and knees and strongly associated with neonatal joint function. LEM increases between POD 1 and POD 5 in fetuses that will have neonatal function.View Large Image Figure ViewerDownload Hi-res image Download (PPT)