MR imaging of multiple gestations

Abstract

With the increasing age of pregnant women and the increasing number of conceptions achieved with use of assisted reproduction technology, there is an increasing number of multifetal pregnancies and an increasing need for prenatal diagnosis and especially for noninvasive diagnostic techniques, including diagnostic imaging techniques. MRI more and more often becomes necessary for counseling parents on treatment options and possible outcomes. Dizygotic twins are always dichorionic (DC). Monozygotic twins may be dichorionic or monochorionic (MC). MC twins may be diamniotic (DA) or monoamniotic (MA). MC twins are at high risk for adverse outcome due to complications related to placental vascular anastomoses: twin-twin transfusion syndrome (TTTS), twin anemia-polycythemia syndrome (TAPS), growth discordance, and twin reversed-arterial-perfusion syndrome (TRAPS). That is why it is chorionicity that determines fetal outcome in twin pregnancies with monochorionic monozygosity being the greatest exposure to anomalies and death. Any congenital malformation seen in a singleton pregnancy can occur in multiple gestation, and its imaging characteristics are the same as described in the previous chapters. MRI of twin pregnancies is more time consuming because there are two fetuses to be examined and evaluated and because twins are much more mobile than singletons, especially in earlier gestation. Twins are not the same as two single fetuses – for example, the normal development of the brains of twins differs from that in singleton pregnancies. This has to be taken into consideration when interpreting the findings and comparing them to the existing atlases or other sources of normal images and measurements’ values.