GNRH1 and vitamin D deficiency: In the subgroup analysis concerning the ovarian stimulation protocols, following adjustment for relevant confounding factors, the clinical pregnancy rate among patients in the GnRH antagonist subgroup without vitamin D deficiency was significantly higher than in both the severe vitamin D deficiency group (adjusted RR = 1.762; 1.025 – 3.028; P = 0.040) and the vitamin D deficiency group (Ref: vitamin D deficiency group; adjusted RR = 1.735; 1.059 – 2.843; P = 0.029).