PLOD1 and vitamin D deficiency: Antral follicle count (AFC) was significantly lower among Asians (WMD − 0.65; 95% CI − 1.28 to − 0.01; P = 0.04; I2 = 0.0%) and luteinizing hormone (LH) levels were higher in non-Asians (WMD 2.16 IU/L; 95% CI 0.20 to 4.12; P = 0.031; I2 = 9.3%) with vitamin D insufficiency/deficiency.