Assisted Reproductive Technology (ART) has been developed to be used for reproductive-age women with primary and secondary infertilities. Obesity is a worldwide epidemic for both women and men and a major global health concern. The direct effect of Body Mass Index (BMI) increase on the outcomes of ART is still unclear. This study aimed to carry out a systematic review of the available scientific evidence to assess the effects of obesity on the clinical outcome of ART treatment. Numerous studies have shown failure in ART due to increased BMIs in infertile women; however, the impact of increased BMI on clinical effectiveness of ART still remains inconclusive. Using results from 44 studies (831616 subjects) we conducted an updated systematic review and meta-analysis to highlight this subject (clinical pregnancy rate, miscarriage rate and live-birth rate). Compared to the women with BMIs of 25 kg/m2 or less, women with BMI ≥ 25 kg/m2 have a lower chance of pregnancy [risk ratio 0.91, 95% CI: 0.89-0.94] as well as lower live-birth rates [risk ratio 0.81, 95% CI: 0.70-0.94], and show increased miscarriage rates [risk ratio 1.35, 95% CI: 1.28-1.46]. Our findings indicate that elevated BMI and obesity requires more recognition as a potential contributor to negative pregnancy outcomes and reduced live-birth following ART. The results of our meta-analysis suggest that weight loss should be considered in overweight and obese women before the initiation of infertility treatment.