[Monochorionic biamniotic twins with a common yolk sac in the first trimester ultrasound scan - is there a higher risk of a congenital defect?]. / Monochoriální biamniální gemini se spolecným zloutkovým váckem pri UZ vysetrení v I. trimestru -je zde zvýsené riziko vrozené vývojové vady?

TYPE OF STUDY: Case report. SETTING: GEST IVF, Centre of Reproductive Medicine, Prague. METHODS: The case report describes pregnancy after IVF + ET. The first trimester ultrasound scan showed monochorionic biamniotic twins with one common yolk sac (YS) only, which is possible in biamniotic twins, but very rare. Identical congenital defects such as anal, coccygeal atresia, and others, were diagnosed prenatally and postnatally in both twins. CONCLUSION: Yolk sac number in monochorionic twins can play an important role in embryogenesi. Any possible relation with certain congenital defects has not yet been described. It is necessary to describe more cases.