Abstract: A new molecular based method for early screening of twin-to-twin transfusion syndrome (TTTS) of monochorionic twin pregnancies is provided in a rapid and non-invasive manner. Using real time quantitative PCR, this method is intended to quantify the expression of HBB, a new TTTS biomarker, in maternal plasma. In pregnant women with this condition, this biomarker is significantly reduced when compared to non-pregnant women, as well as pregnant women with both single and twin pregnancies without pathology. This method, if applied to all women with monochorionic twin pregnancies, will allow early screening of TTTS, benefiting both the mother and the fetuses, which can more quickly take advantage of an effective treatment with predictable improvement in fetuses' survival.