Melatonin improves fertilization rate in assisted reproduction: Systematic review and meta-analysis

•Melatonin had beneficial effects on outcomes in assisted reproductive technologies, but it had no influence on pregnancy.•Melatonin had beneficial effects such as the improvement in the fertilization rate.•Melatonin has a beneficial effect on the formation of mature oocytes (MII). Melatonin is a hormone produced by the pineal gland and it has antioxidant properties. This study aimed to evaluate the effects of melatonin on assisted reproductive technologies through a systematic review and a meta-analysis. Search strategies were used in PubMed and in other databases covering the last 15 years. After screening for eligibility, 17 articles were selected for the systematic review. For the meta-analysis statistics, two groups were formed, the treatment group (with melatonin) and the control group (without melatonin) for various assisted reproduction outcomes. The main results were that no statistical differences were found concerning the clinical pregnancy outcome (p = 0.64), but there was a statistical difference with respect to Mature Oocytes (MII) (p = 0.001), antral follicle count (p = 0.0002), and the fertilization rate (p ≤ 0.0001). Melatonin had beneficial effects such as the improvement in the fertilization rate, although the authors did not obtain significance in the clinical pregnancy rate.