OBJECTIVE: This study aimed to compare the coagulation and platelet parameters in women with spontaneous premature ovarian insufficiency (POI) with those in age-matched controls. METHODS: This case-control study recruited 202 women with POI and 202 age-matched women with benign gynecological diseases as controls. Coagulation parameters, including prothrombin time (PT), international normalized ratio (INR), activated partial thromboplastin time (APTT), and thrombin time (TT), fibrinogen, and platelet parameters, including platelet count (PLT), mean platelet volume (MPV), plateletcrit (PCT), and platelet distribution width (PDW), were compared between women with POI and controls. Factors associated with coagulation and platelet parameters were also analyzed in women with POI. RESULTS: In women with POI, higher fibrinogen levels and PDW, lower PLT, MPV, and PCT levels, and shorter TT were observed (p <
0.001). Linear regression analysis further revealed that women with POI were more likely to exhibit increased serum fibrinogen levels (β = 0.465, 95% confidence interval [CI] 0.366-0.564) and PDW (β = 0.340, 95% CI 0.300-0.379), decreased TT (β = -1.101, 95% CI -1.233--0.969), PLT (β = -50.985, 95% CI -65.087--36.882), MPV (β = -1.498, 95% CI -1.875 to -1.120), PCT levels (β = -0.084, 95% CI -0.095--0.973). Additionally, follicle-stimulating hormone levels were positively associated with fibrinogen levels in women with POI. There were no statistically significant differences in PT, INR, and APTT between women with POI and controls. CONCLUSIONS: Women with POI exhibited decreased platelet numbers, abnormal platelet morphology, and elevated fibrinogen concentrations, potentially implicating POI's etiopathogenesis or contributing to an increased risk of cardiovascular disease in women with POI. No coagulation abnormalities were observed in women with POI.