Reversal of Fetofetal Transfusion Syndrome in a Monochorionic Triamniotic Triplet: A Case Report

In monochorionic multiple pregnancies, each fetus has its own amniotic sac but shares a single placenta. Along the placental surface, fetal vessels not only supply blood individually but also form anastomoses that cross between sacs, creating shared circulation. Such inter-fetal vascular connections can result in unequal blood volumes, a phenomenon termed "fetofetal transfusion" syndrome (FFTS). This imbalance is well-known in monochorionic diamniotic (MD) twins as twin‑twin transfusion syndrome, where the recipient fetus, subjected to volume overload, is at risk of heart failure, while the donor fetus experiences circulatory depletion. Diagnosis relies on discordant amniotic fluid levels: polyhydramnios in the recipient and oligohydramnios in the donor. Similar hemodynamic effects have been observed in monochorionic triamniotic (MT) triplet pregnancies. Reversal of FFTS is also well-documented in MD twin pregnancies; however, reports on a similar phenomenon occurring in MT triplet pregnancies are scarce in the literature. We encountered a case of FFTS in an MT triplet pregnancy in which it was suggested that reversal of FFTS occurred. At 19 weeks of gestation, one fetus (Fetus A) presented with polyhydramnios, whereas the other two fetuses (Fetuses B and C) exhibited oligohydramnios, fulfilling the criteria for FFTS. The patient experienced abdominal distension and cervical shortening, prompting amnioreduction. After serial procedures, an accidental amniotic septostomy between Fetuses A and C occurred as a procedural complication. Around the same time, the increase in amniotic fluid volume halted, and Fetus B, initially an oligohydramniotic fetus uninvolved in the septostomy, developed tricuspid regurgitation and right ventricular hypertrophy, along with increased amniotic fluid volume. Although this increase did not meet the criteria for polyhydramnios, which is required for FFTS diagnosis, the fetal echocardiographic findings and the postnatal symptoms of polyuria and hypertension suggested that reversal of FFTS may have occurred. A cesarean section was performed at 28 weeks of gestation due to Doppler abnormalities in Fetus C, and all three neonates were discharged without severe neurological sequelae. Following the septostomy, assessment of individual amniotic fluid volumes became infeasible, precluding definitive determination of donor-recipient status. However, the resolution of oligohydramnios in the initial donor Fetus B and the emergence of cardiac overload suggest the possibility of acute inter-fetal blood redistribution from either Fetus A or C. Although Fetus B did not meet the formal diagnostic criterion for polyhydramnios, postnatal symptoms support the hypothesis of reversal of FFTS. This case illustrates the potential for reversal of FFTS in MT triplet pregnancies and suggests that procedures such as amnioreduction or septostomy may serve as triggering events. Our findings also underscore the importance of fetal echocardiography in assessing donor-recipient status, particularly when traditional diagnostic criteria based on amniotic fluid volume become unreliable.