To investigate the association of the myelomeningocele (MMC) volume with prenatal and postnatal motor function (MF) in cases who underwent a prenatal repair. Retrospective cohort study (11/2011 to 03/2019) of 63 patients who underwent a prenatal MMC repair (37 fetoscopic, 26 open-hysterotomy). At referral, measurements of the volume of MMC was performed based on ultrasound scans. A large MMC was defined as greater than the optimal volume threshold (ROC analysis) for the prediction of intact MF at referral (2.7 cc). Prenatal or postnatal intact motor function (S1) was defined as the observation of plantar flexion of the ankle based on ultrasound scan or postnatal examination. 23/63 participants presented a large MMC. Large MMC lesions was associated with an increased risk of having clubfeet by 9.5 times (CI%95[2.1-41.8], p < 0.01), and reduces the chances of having an intact MF at referral by 0.19 times (CI%95[0.1-0.6], p < 0.01). At birth, a large MMC reduces the chance of having an intact MF by 0.09 times (CI%95[0.01-0.49], p < 0.01), and increases the risk of having clubfeet by 3.7 times (CI%95[0.8-18.3], p = 0.11). A lower proportion of intact MF and a higher proportion of clubfeet pre- or postnatally were observed in cases with a large MMC sac who underwent a prenatal repair.Trial registration: Clinicaltrials.gov NCT02230072 and NCT03794011 registered on September 3rd, 2014 and January 4th, 2019.