Spontaneous twin anemia-polycythemia sequence from two donors to one recipient in a monochorionic triamniotic pregnancy: Case report and review of the literature.

Monochorionic triamniotic (MCTA) pregnancies present a high number of complications, mainly due to the presence of unbalanced vascular anastomoses, such as twin anemia-polycythemia sequence (TAPS). Previous reported cases related to TAPS are in twin pregnancies or only affect the monochorionic component of dichorionic triamniotic (DCTA) pregnancies. We report an exceptional case, the only one reported as far as we know, of a MCTA pregnancy that developed a TAPS in which the three triplets are implicated, from two donors to one recipient. The pregnancy had been previously sonographically diagnosed as DCTA pregnancy and this could not explain the clinical results. The pathological study of the placenta showed the presence of three monochorionic dividing membranes, a congested area in the recipient parenchyma and two non-congested areas in the donor's parenchyma that confirmed the clinical findings. Pathological study of multiple placentas should always be done because it provides understanding of pregnancy complications.