Introduction: To compare tocolysis with magnesium sulfate versus atosiban regarding the occurrence of short-term preterm labor and maternal side effects during and after open fetal myelomeningocele (MMC) repair. Material and Methods: A prospective nonrandomized cohort study was performed including 30 fetal MMC cases. The first 15 cases (group 1) received magnesium sulfate according to the MOMS protocol. In the following 15 cases (group 2), magnesium sulfate was substituted by atosiban. Chorioamniotic membrane separation (CMS), premature prelabor rupture of the fetal membranes (PPROM), preterm delivery <3 weeks after fetal MMC repair, and maternal complications due to the tocolytic medication were the major endpoints. Results: In both groups, one CMS but no PPROM was diagnosed <3 weeks after fetal MMC repair. One patient of group 2 delivered <3 weeks after fetal MMC repair because of an intraoperative placental abruption at 25 weeks. All women of group 1 showed an electrolyte imbalance during magnesium sulfate administration. One woman of group 1 developed several episodes of a third-degree atrioventricular block within the first 3 days after fetal surgery. Lethargy was found in all women during magnesium sulfate therapy. No maternal side effects were found under atosiban. Discussion: The use of atosiban resulted in an almost identical short-term uterine outcome without any serious maternal complications as seen when magnesium sulfate was given. Thus, the authors suggest using atosiban instead of magnesium sulfate in the context of open fetal surgery.