U-shaped Association of Third-trimester Serum Uric Acid with Postpartum Hemorrhage: Statistical Mediation Effects of Hemoglobin, Fibrinogen, and D-dimer—A Multicenter Cohort Study

Serum uric acid, a key metabolic marker, has been linked to pregnancy complications, yet its association with postpartum hemorrhage (PPH)—especially non-linear relationships and underlying mechanisms—remains uninvestigated. We conducted a multicentre cohort study (pregnant women) and nested case-control study (1:2 matching) in China (2017–2024). Third-trimester serum uric acid was measured. PPH was defined per World Health Organization criteria (≥500 mL vaginal/≥1000 mL cesarean blood loss). Logistic regression, restricted cubic spline (RCS) analysis, mediation analysis, and predictive model evaluation were performed. In the cohort, serum uric acid was stratified into quintiles (Q1: