PGF and preeclampsia: At present, the serum markers used to screen for preeclampsia in twin pregnancies mainly include pregnancy-associated plasma protein A, placental protein 13, placental growth factor (Maymon et al., 2017), inhibin A, and unconjugated estriol (Kim et al., 2019); however, widespread roll-out of these indicators is difficult to develop and promote in underdeveloped areas.