This article addresses a gap in the literature by exploring legal mobilization on abortion issues in an international human rights context. The authors explore what happens to social movement claims when they reach international human rights courts, and what ongoing repercussions for human rights might result. In order to do this, they use the landmark IVF case Gretel Artavia Murillo et al. v Costa Rica tried at the inter-American Court of Human Rights. Through the case analysis, the authors show how legal mobilization before international human rights courts can moderate social movement claims within the legal arena. In Gretel Artavia, conservative and feminist rivals must respond to each other’s submissions and argue within the frame of the courts’ norms and language. The authors demonstrate that such contentious engagement ultimately served to legitimate the inter-American system by forcing opposing movements to engage with and address each other’s arguments to a far greater extent than ever before.