PGF and preeclampsia: PROGNOSIS derived and validated a cut-off value of 38 whereby: a sFlt-1/PlGF ratio ≤ 38 rules out the occurrence of preeclampsia in the next week with a negative predictive value (NPV) of 99.3% (and 97.9% for rule out within 2 weeks), and a ratio > 38 indicates that there is an increased risk of developing preeclampsia in the next 4 weeks [26, 29].