Acardiac anomaly is a rare complication of multiple pregnancies. Arterial-to-arterial vascular anastomoses between twins, in the presence of a fused placenta, develop in the first trimester. Consequently the pump twin provides the acardius with blood. The second case of acardiac twin pregnancy with cytogenetic analysis of the acardiac showing the karyotype 47,XX,+2 is presented. Literature of acardiac twin pregnancies with different cytogenetic results and cases with trisomy 2 are reviewed, and a hypothesis of genesis is put forward.