Twin pregnancy and the risk of preeclampsia: bigger placenta or relative ischemia?

In twin pregnancies, circulating sFlt1 levels and sFlt1/PlGF ratios were twice as high as those in singleton pregnancies. The increased serum sFlt1 levels in twin pregnancies were not accompanied by any changes in the levels of sFlt1 mRNA and HIF-1α protein in the twin placentas but were correlated with increased placental weight. These findings suggest that the increased risk of preeclampsia in twin pregnancies may be due to increased placental mass that leads to increased circulating levels of sFlt1.