Introduction: Regarding its pathogenesis, discordant development in early gestation, as well as vascular anastomoses between twins are postulated to be required for the establishment of the twin-reversed arterial perfusion (TRAP) sequence. However, first trimester findings associated with this complication have not yet been reported.
Case: A discordant monochorionic twin was revealed upon examination of a 24-year-old primigravida at 11 weeks' gestation. Cystic masses were identified on the back of the smaller twin, later followed by the appearance of skin edema and pericardial effusion, indicating cardiac failure. Subsequently, despite diagnosis of fetal demise at 15 weeks the lower body was shown to have further developed and the heartbeats appeared again, resulting in an acardia anceps or hemicardia. No remarkable change was observed in the larger normal twin.
Conclusion: This occurrence was considered consistent with the current hypothesis regarding the pathogenesis of the acardiac anomaly. First trimester discordancy in a monochorionic twin gestation is considered to represent an early manifestation of TRAP sequence.
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