PGF and preeclampsia: However, since the sFLT1 and PlGF concentrations are normally proportional to each other and their ratio is relatively constant until term (~37 weeks) in a normal pregnancy, and because sFLT1 concentrations rise disproportionately during development of preeclampsia, measurement of the sFLT1/PlGF ratio becomes a highly predictive test to assess risk of developing preeclampsia and its related complications.