PGF and twin to twin transfusion syndrome: In MCDA twins complicated by untreated TTTS, we have demonstrated that the second-trimester maternal serum concentrations of AFP and the ratio of sFlt-1 to PlGF were significantly higher in TTTS compared to gestationally matched uncomplicated MCDA twins [16, 17]; however, there has been little research on the prognostic ability of first-trimester maternal serum [18].