Feminists and religious conservatives across the globe have increasingly turned to courts in their battles over abortion. Yet while a significant literature analyzes legal mobilization on abortion issues, it tends to focus predominantly on domestic scenarios. In this article, we consider the effects of this contentious engagement of pro-choice and anti-abortion movements in international human rights fora, asking what happens to social movement claims when they reach international human rights courts. We answer the question through a detailed description of a single case, Gretel Artavia Murillo et al. v. Costa Rica, decided by the Inter-American Court of Human Rights in 2012 but with ongoing repercussions for abortion rights, given its authoritative interpretation of embryonic right to life. Through our analysis of Artavia Murillo, we show how legal mobilization before international human rights courts moderates social movement claims within the legal arena, as rivals respond to one another and argue within the frame of courts' norms and language.