Twins account for 10% of perinatal mortality, although they represent only 3.0% of pregnancies [1]. Twin pregnancy has a more complicated course in utero than singletons, and management is also complicated by the fact that more than one fetus must be taken into account. Approximately 30% of twins are monozygotic and 70% are dizygotic [2]. The key to management of multiple pregnancies is the accurate determination of chorionicity. This is best performed in the first trimester when accuracy rates approach 100% [3]. If monochorionic (MC)
twins have been confirmed, then some unique com- plications mentioned in this article should be kept in mind before performing sonographic examina- tion. These complications include twin–twin trans- fusion syndrome (TTTS), twin reversed arterial perfusion (TRAP), MC twins with selective intrauter- ine growth restriction (IUGR), and MC twins with one anomaly.
Common obstetric complications, such as preeclampsia, gestational diabetes, preterm labor, and intrauterine fetal growth restriction, occur more frequently in multiple gestations, yet the diagnosis and management of these conditions are similar tothose in singleton pregnancies [4]. MC twins run the highest risk of complications and the wellbeing of one fetus crucially depends on that of the other because of the almost ever-present vascular anasto- moses in the common placenta [3]. Management of the unique complications of MC twins are also influ- enced by the vascular anastomoses on the chorionic plate.ThesecomplicationsincludeTTTS,TRAP,IUGR, and MC twins with one anomaly. Diagnosis of these unique complications of MC twin pregnancy depend heavily on ultrasonography, and manage- ment would largely be dependent on the sono- graphic guide procedures.