[Twin pregnancy with a complete hydatiform mole and a viable co-twin].

A complete hydatiform mole coexisting with a live, viable twin is a rare event. The diagnosis is challenging, and is normally achieved only at second trimester. It may be associated with thyrotoxicosis, vaginal bleeding, preeclampsia, fetal death or persistent throphoblastic disease. The authors describe the case of a pregnant woman presenting with first trimester bleeding. Ultrasound revealed a twin pregnancy with a viable twin and another placenta apparently detached. At 16 gestational weeks ultrasound revealed a live fetus with a normal placenta and a separate vacuolated and vascularized mass. Facing the hypothesis of gestational trophoblastic disease, the couple chose pregnancy interruption. Given the rarity of this situation, a high index of suspicion is needed to achieve the diagnosis. Despite the existence of case reports with good fetal and maternal outcome, the decision of pregnancy continuation should be made by the informed parents.