FLT1 and twin to twin transfusion syndrome: We quantified plasma levels of VEGF-R1, VEGF-R2, IL-1β, IL-6 and IL-8 in twin pregnant women with (n=53) and without TTTS (n=72) and in women with single pregnancy (n=30) by ELISA and analyzed the association of maternal circulating biomarker levels with TTTS.