Perinatal Outcomes of Monochorionic-Diamniotic Twin Pregnancies Uncomplicated at 28 Weeks of Gestation.

We examined the prevalence of specific perinatal complications of monochorionic-diamniotic twin pregnancies in cases without any abnormal findings until the second trimester of pregnancy. This was a retrospective cohort study performed at a tertiary perinatal center in Tokyo, Japan. There were 88 cases of uncomplicated monochorionic-diamniotic twin pregnancies at 28 weeks of gestation. In five of them (5.7%), there were serious complications associated with placental circulatory imbalance between the twins during the third trimester of pregnancy. Two cases were complicated by twin-twin transfusion syndrome, two cases were complicated by twin anemia-polycythemia sequence, and one case was complicated by acute twin-twin transfusion syndrome. In the five cases, no abnormal ultrasonographic findings or symptoms were recognized one or two weeks prior to the diagnosis. Fifty-eight cases (65.9%) were delivered at term uneventfully. Serious complications due to placental circulatory imbalance between twins occurred in about 6% of cases during the third trimester of pregnancy.