The modern era of fetal surgical interventions began in the 1980s, when improved ultrasonographic imaging enabled prenatal detection of life-limiting birth defects.1 However, the rarity of many severe fetal anomalies, maternal complications associated with open fetal interventions, and the availability of effective, if imperfect, strategies for postnatal infant care restricted the performance of informative clinical trials.1 The Management of Myelomeningocele Study (MOMS),2 the results of which were reported in 2011, served as an early example of the importance of randomized clinical trials in assessing the benefits and risks of fetal interventions that had previously been performed largely on the basis . . .