Endothelial dysfunction is an important component of preeclampsia like premature ovarian insufficiency (POI), and it is reported that placental growth factor (P1GF) and soluble fms-like tyrosine kinase receptor-1 (sFlt-1) levels are important in preeclampsia. Extra-placental sources for P1GF and sFlt-1 have also been identified, including various cell types. In animal models of POI, niacin treatment inhibited follicular apoptosis under hazardous conditions while significantly reducing cumulus cell apoptosis. The number of developing follicles also increased after niacin was given. This study was designed to determine blood sFlt-1, P1GF, and niacin concentrations in women with idiopathic POI (iPOI) compared with those of healthy women. The study comprised 45 women with iPOI and 45 healthy women. Blood was obtained and analyzed at the early follicular phase of the menstrual cycle and sFlt-1, P1GF, and niacin levels were measured using a commercially available enzyme-linked immunosorbent assay kit. No significant differences were observed in the two groups according to the gravidity numbers, parity, abortion, live births, and menarche ages (p ≥ 0.05). In the iPOI group, the mean anti-mullerian hormone value was 0.03 ± 0.04 (min-max, 0.00-0.21)ng/ml. sFlt-1, P1GF, niacin levels, and also the sFlt-1/P1GF ratio were lower in the iPOI group (p < 0.01). A significant discriminative role of sFlt-1, P1GF, niacin levels, and the sFlt-1/P1GF ratio for the presence of iPOI, with cut-off values of 5.13, 10.28, 37.17, and 0.61 ng/ml, respectively, were reported in the receiver operating characteristics curve analysis. Lower levels of P1GF, sFlt-1, niacin, and sFlt-1/P1GF ratios may be associated with the development of POI/iPOI. Further studies are required to better understand the etiopathogenesis of POI/iPOI. NCT04641624 (clinicaltrials.gov).