The development of an acardiac anomaly, one of the most severe human malformations, is a rare complication unique to monochorionic multiple pregnancies. In this condition, the primary malformation is the lack of a well-defined cardiac structure in one twin (the acardiac twin), which is kept alive by its structurally normal co-twin (the pump twin).

The final diagnosis for a twin pregnancy with an acardiac twin may be established after the 9th week, when the cephalic extremity and limbs can be precisely determined.

Direct signs that lead to the diagnosis of an acardiac twin include the absence of cardiac and fetal movements, difficult visualization of the trunk and cephalic poles, thickening of subcutaneous tissue and the presence of umbilical artery reverse flow towards the acardiac fetus mass. The pump fetus may demonstrate hydramnios, cardiomegaly and heart failure.

Once an acardiac anomaly is diagnosed, both the acardiac and pump twins should be assessed to classify the pregnancy according to prognostic factors based on the size and growth of the acardiac twin and the cardiovascular condition of the pump twin. Assessing the extent of heart damage in the pump fetus is a key step in pregnancy management.

There are two available options, either conservative or interventional, for the management of these pregnancies. Serial ultrasound surveillance is important for detecting any worsening of the condition, which may suggest the need for interventions to optimize the pump-twin's chance for survival.

We performed a retrospective analysis of three cases of monochorionic twin pregnancies diagnosed with a twin reversed arterial perfusion (TRAP) sequence during the first and second trimesters. We compared our data with those offered by a review of the literature.