PGF and preeclampsia: Both associations were highly statistically significant (P = 2.5 × 10–6 and 1.1 × 10–6, respectively) and were unaffected by adjustment for the soluble fms-like tyrosine kinase receptor 1 to placental growth factor ratio (sFLT1:PlGF, an existing placental biomarker for preeclampsia; refs. 21, 22), the sex of the fetus, and maternal characteristics (Figure 5, B–D).