PGF and twin to twin transfusion syndrome: Decreased maternal serum PlGF measured in the first trimester was associated with the development of TTTS before adjustment (OR 0.43 [95%CI 0.20, 0.91]), and this remained after adjustment for previously identified prognostic factors (aOR 0.42 [95%CI 0.19, 0.93], p = 0.03), demonstrating an estimated 42% increase in the odds of TTTS for each concentration unit decrease in loge-PlGF.