Background: Myomectomy has potential risks of complications. To reduce these risks, medical pre-treatment can be applied to reduce fibroid size and thereby potentially decrease intra-operative blood loss, the need for blood transfusion and emergency hysterectomy. The aim of this systematic review and meta-analysis is to study the effectiveness of medical pre-treatment with Gonadotropin-releasing hormone agonists (GnRHa) or ulipristal acetate prior to laparoscopic or laparotomic myomectomy on intra-operative and post-operative outcomes. Methods: We performed an extensive search in Embase.com, Wiley/Cochrane Library and PubMed in accordance with the Prisma guidelines. All studies published as full papers in peer reviewed journals using GnRHa or ulipristal acetate as medical pre-treatment independent of route of administration or dosage before laparotomic or laparoscopic myomectomy were included. The primary outcome was duration of surgery. Secondary outcomes were duration of enucleation, blood loss, degree of difficulty of surgery, identification of cleavage planes, proportion of vertical incisions, conversion rate, frequency of blood transfusions, post-operative complications, duration of hospital stay, frequency of recurrence of fibroids, frequency of uterine adhesions, recovery time and quality of life. No language restrictions were applied. Meta-analysis were performed where possible. Findings: Twenty-three studies were included. In laparotomic myomectomy, pre-treatment with GnRHa decreases intra-operative blood loss with 97.39ml (95% CI -111.80 to -82.97) compared to no pre-treatment or placebo. Pre-treatment with GnRHa before laparoscopic myomectomies also shows a reduction in intra-operative blood loss by 23.03ml (95% CI -40.79 to -5.27) and in the frequency of blood transfusions (OR 0.17, 95% CI 0.05 to 0.55) compared to no pre-treatment. Only two retrospective cohort studies reported on pre-treatment with ulipristal acetate compared to no pre-treatment before laparoscopic myomectomy showing a statistically significant reduction in intra-operative blood loss, duration of surgery and frequency of blood transfusions after pre-treatment with ulipristal acetate. Conclusion: Administration of GnRHa prior to laparotomic myomectomy reduces blood loss and might decrease uterine adhesion formation. Pre-treatment with GnRHa before laparoscopic myomectomy reduces blood loss, the frequency of blood transfusions and might increase recurrence rate of fibroids, however it should be taken into account that some results are mainly based on cohort studies. Other pre-treatment agent ulipristal acetate has not been investigated sufficiently for relevant surgical outcomes.