Conservative Catholics have launched a barrage of challenges to Pope Francis before a big Vatican meeting beginning on Wednesday, with five cardinals demanding clarifications on same-sex couples and other issues, and a women's group saying only men should vote at the event. The cardinals from Asia, Europe, Africa, the United States and Latin America said on Monday they had sent the pope a set of formal questions, known as "dubia" ("doubts" in Latin), about the gathering. In an open letter to Catholics, they said they had announced their challenges "so that you may not be subject to confusion, error, and discouragement but rather may pray for the universal Church". This comes as women are expected to vote at the Synod for the first time in the history of the church.