Background: In the context of increasing rates of overweight and obesity in young adult women, and the increasing numbers of women seeking help for fertility problems, it is important to understand whether physical activity (PA) could help with management of reproductive health problems, with or without weight loss. Objective and rationale: The primary aim of this systematic review and meta-analysis was to assess the effects of PA on selected reproductive health outcomes in young adult women, in order to inform best practice advice for women in terms of promoting fertility and reproductive health in young adulthood. Search methods: An electronic search of PubMed, EMBASE, MEDLINE, Cumulative Index to Nursing and Allied Health Literature, PsycINFO, Web of Science, SportDiscus, and Cochrane was performed for studies published between January 2000 and May 2018. Keywords and Medical Subject Headings terms related to PA, reproductive health, and weight gain were used. Studies were selected if they were intervention studies, if PA was delivered as part of an intervention to pre-menopausal women, and if any reproductive health outcome was reported. Quality analysis was performed using the Tool for the assEssment of Study qualiTy and reporting in EXercise. Outcomes: Eighteen studies, with a mix of four types of study design (4 randomized controlled trials (RCTs), 11 randomized comparison trials, 2 non-randomized comparison trials, and 1 single-arm clinical trial), were identified. Comparisons included fertility treatment (four studies) and common treatments for women with polycystic ovary syndrome (PCOS) symptoms (nine studies). Pooled analysis of data from three of the four studies with a control group showed higher pregnancy [risk ratio (RR) 2.10, 95% CI (1.32, 3.35); three studies] and live birth [RR 2.11, 95% CI (1.02, 4.39); two studies] rates in the intervention groups compared with non-therapy controls. Aggregated data from the fertility treatment comparative studies (i.e. those that compared PA with standard fertility treatment such as clomiphene, gonadotrophins, and/or IVF) showed no significant intervention differences: RR 1.46, 95% CI (0.87, 2.45) for clinical pregnancy (four studies) and RR 1.09, 95% CI (0.56, 2.12) for live births (two studies). Pooled analysis from the comparison trials that used pharmaceutical or dietary treatment for PCOS as comparison showed higher pregnancy rates [RR 1.59, 95% CI (1.06, 2.38); five studies] and live birth rates [RR 2.45, 95% CI (1.24, 4.83); two observations] in the PA intervention groups than in the comparison groups. Analysis of other outcomes, such as ovulation rates, menstrual regularity, and conception rates, showed no differences between the PA intervention and comparison groups. Wider implications: There is emerging evidence from RCT that PA may improve pregnancy rates in women with reproductive health problems. Comparative studies indicate that PA intervention may be as effective as other commonly used clinical intervention strategies for improving reproductive health outcomes. While the type, intensity, frequency, and duration of optimal PA intervention, and the role of PA independent of weight loss, remain unclear, these preliminary findings suggest that PA may be an affordable and feasible alternative or complementary therapy to fertility treatments.