OBJECTIVE: To systematically review the performance of soluble fms-like tyrosine kinase-1 (sFlt-1), placental growth factor (PlGF), and the sFlt-1/PlGF ratio in predicting adverse outcomes in women with preeclampsia. DATA SOURCES: We performed a systematic search of MEDLINE, EMBASE, CINAHL, Cochrane, Scopus, ClinicalTrials.gov, and Emcare databases from 1989 to March 2019 to identify studies correlating sFlt-1, PlGF, and the sFlt-1/PlGF ratio with the occurrence of adverse outcomes in women with preeclampsia. METHODS OF STUDY SELECTION: Two independent reviewers screened 3,194 studies using Covidence. Studies were included if they examined the performance of sFLT-1, PlGF, or the sFLT-1/PlGF ratio in predicting adverse outcomes in women with suspected or confirmed preeclampsia. TABULATION, INTEGRATION, AND RESULTS: We extracted contingency tables with true-positive, false-positive, true-negative, and false-negative results. We calculated sensitivity, specificity, diagnostic odds ratios, and area under the summary receiver operating characteristic curve (area sROC) through a bivariate mixed-effects meta-analysis. Our literature search identified 3,194 articles, of which 33 (n=9,426 patients) were included. There was significant variation in the included studies with regard to the biomarkers and outcomes assessed. As such, few studies (n=4-8) were included in the meta-analysis component with significant heterogeneity between studies (I2=33-99). Nonetheless, both PlGF and the sFlt-1/PlGF ratio demonstrated area sROC values between 0.68 and 0.87 for the prediction of composite adverse maternal and perinatal outcomes, preterm birth and fetal growth restriction. CONCLUSION: Placental growth factor and the sFlt-1/PlGF ratio show prognostic promise for adverse outcomes in preeclampsia, but study heterogeneity limits their clinical utility. SYSTEMATIC REVIEW REGISTRATION: PROSPERO, CRD42019136207.