Twin Anemia-Polycythemia Sequence With Spontaneous Resolution in Dichorionic Diamniotic Twin Pregnancy: A Case Report and a Review of the Literature.

Complications of twin pregnancy such as twin anemia-polycythemia sequence (TAPS), which involve placental anastomotic vessels, occur mostly in monochorionic diamniotic twins and they have rarely been reported in dichorionic diamniotic (DD) twins. Here, we report a case of DD twins diagnosed with TAPS with fetal hydrops caused by fetal anemia at 28 weeks, which resolved spontaneously during pregnancy. A 37-year-old pregnant woman was referred to our hospital because of a twin pregnancy at 13 weeks. The fetus showed the lambda sign, leading to the diagnosis of DD twin. At 28 weeks, fetal ascites and subcutaneous edema were observed in twin A. In blood flow assessment, elevated middle cerebral artery peak systolic velocity (MCA-PSV) 88.0 cm/s (2.3 MoM), pulsatile flow in the umbilical vein, and increased flow in the ductus venosus were also found, but no abnormal flow in the umbilical artery was found in twin A. In contrast, there were no signs of hydrops and MCA-PSV was 38.7 cm/s (1.0 MoM) in twin B. Both fetuses did not show any abnormality of amniotic fluid volume. Thus, the twin was diagnosed with TAPS in DD twins. Fetal hydrops could be resolved spontaneously, and MCA-PSV gradually decreased. Two female infants weighing 2,366 g and 2,048 g were delivered by cesarean section at 35 weeks. Blood tests demonstrated Hb 8.5 g/dl and reticulocyte 7.4% in twin A and Hb 13.3 g/dl and reticulocyte 6.1% in twin B, respectively. This case highlights that complications of twin pregnancy involving placental anastomotic vessels such as TAPS could occur even in DD twins.