Very Early and Simple Determination of Chorionic and Amniotic Type in Twin Gestations by High-Frequency Transvaginal Ultrasonography

OBJECTIVE: The aim was to determine the chorionic and amniotic types in multifetal pregnancies with transvaginal ultrasonography at very early stage of gestation. STUDY DESIGN: Twenty-one spontaneous multifetal pregnancies were scanned transvaginally before 8 weeks' gestation (four of them from 4th week). The chorionic and amniotic type was determined ultrasonographically. All twin gestations had postpartum pathologic evaluation of the placenta and histologic determination of the chorionic and amniotic type. RESULTS: Ultrasonographic evaluation of the 21 pregnancies demonstrated 20 twin and 1 triplet gestation. Four of the twin pregnancies were monochorionic-diamniotic. Triplet was monochorionic-triamniotic (spontaneously aborted in 8th week of gestation). In all 20 twin pregnancies, transvaginal ultrasonography correctly predicted the chorionic and amniotic type before 8 weeks of gestation. CONCLUSION: Transvaginal ultrasonography allows a reliable, simple and rapid determination; the dichorionic twin pregnancy in 4 weeks, monochorionic in 5 weeks, and differentiation of mono- or diamniotic in 7 weeks of gestation.