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As the number of overweight and obese women seeking assisted reproductive care increases, interest in understanding the effects of excess weight on fertility is also increasing. Therefore, a systematic review and meta-analysis were performed to evaluate the associations of overweight and obesity with assisted reproductive technology outcomes. The following databases were searched through March 2019: MEDLINE (PubMed), Embase, Scopus, Lilacs, Web of Science, Clinical Trials and SciELO. The keywords used were obesity, overweight and assisted reproduction, as well as similar terms. Articles were selected based on titles and abstracts. Potentially relevant studies were evaluated for inclusion by two reviewers. Subsequently, quality was assessed using the Newcastle-Ottawa Quality Assessment Scale. The meta-analysis was performed using a random-effects model. Sensitivity analyses were performed to investigate sources of heterogeneity, as recommended by the Cochrane Collaboration. In total, 53 studies with 1,445,406 treatment cycles were included. When analysing one cycle per patient, being overweight or obese was found to have a weak negative impact on clinical pregnancy, livebirth and miscarriage rates; number of mature oocytes; duration of ovarian stimulation; and gonadotropin dosage used among the exposed women. Therefore, an increased body mass index is associated with weak adverse outcomes among women undergoing in-vitro fertilization or intracytoplasmic sperm injection. This study searched a greater number of research databases and analysed a greater number of studies with good methodological quality and low or moderate heterogeneity, including a greater number of assisted reproduction treatment cycles, than other studies conducted to date. Nevertheless, more robust studies on the subject are needed to elucidate other aspects related to exposure and outcomes., (Copyright © 2022 Elsevier B.V. All rights reserved.)