Abstract: We included eight parallel-design RCTs, involving a total of 640 participants. We did not assess any of the studies as being at low risk of bias across all domains, with the main limitation being lack of blinding. Using GRADE methodology, the quality of the evidence ranged from very low to low quality. Long-term GnRH agonist therapy versus no pretreatment We are uncertain whether long-term GnRH agonist therapy affects the live birth rate (RR 0.48, 95% CI 0.26 to 0.87; 1 RCT, n = 147; I2 not calculable; very low-quality evidence) or the overall complication rate (Peto OR 1.23, 95% CI 0.37; to 4.14; 3 RCTs, n = 318; I2 = 73%; very low-quality evidence) compared to standard IVF/ICSI. Further, we are uncertain whether this intervention affects the clinical pregnancy rate (RR 1.13, 95% CI 0.91 to 1.41; 6 RCTs, n = 552, I2 = 66%; very low-quality evidence), multiple pregnancy rate (Peto OR 0.14, 95% CI 0.03 to 0.56; 2 RCTs, n = 208, I2 = 0%; very low-quality evidence), miscarriage rate (Peto OR 0.45, 95% CI 0.10 to 2.00; 2 RCTs, n = 208; I2 = 0%; very low-quality evidence), mean number of oocytes (MD 0.72, 95% CI 0.06 to 1.38; 4 RCTs, n = 385; I2 = 81%; very low-quality evidence) or mean number of embryos (MD -0.76, 95% CI -1.33 to -0.19; 2 RCTs, n = 267; I2 = 0%; very low-quality evidence). Long-term GnRH agonist therapy versus long-term continuous COC No studies reported on this comparison. Long-term GnRH agonist therapy versus surgical therapy of endometrioma No studies reported on this comparison. This review raises important questions regarding the merit of long-term GnRH agonist therapy compared to no pretreatment prior to standard IVF/ICSI in women with endometriosis. Contrary to previous findings, we are uncertain as to whether long-term GnRH agonist therapy impacts on the live birth rate or indeed the complication rate compared to standard IVF/ICSI. Further, we are uncertain whether this intervention impacts on the clinical pregnancy rate, multiple pregnancy rate, miscarriage rate, mean number of oocytes and mean number of embryos. In light of the paucity and very low quality of existing data, particularly for the primary outcomes examined, further high-quality trials are required to definitively determine the impact of long-term GnRH agonist therapy on IVF/ICSI outcomes, not only compared to no pretreatment, but also compared to other proposed alternatives to endometriosis management.

Plain-language summary: We found eight randomised controlled trials comparing long-term GnRH agonist therapy with no pretreatment including a total of 640 women with endometriosis prior to IVF/ICSI. The evidence is current to January 2019. Compared to no pretreatment, we are uncertain whether long-term GnRH agonist therapy prior to IVF/ICSI in women with endometriosis affects the live birth rate. The evidence suggests that if the chance of live birth rate is assumed to be 36% with no pretreatment, the chance following long-term GnRH agonist therapy would be between 9% and 31%. We are also uncertain whether this intervention affects complication rate, clinical pregnancy rate, multiple pregnancy rate, miscarriage rate, mean number of oocytes and mean number of embryos. No studies compared long-term GnRH agonist therapy to long-term continuous COC therapy or surgery to remove endometriomas. The evidence was of very low quality. The main limitations in the evidence were lack of blinding (the process where the women participating in the trial, as well as the research staff, are not aware of the intervention used), inconsistency (differences between different studies) and imprecision (random error and small size of each study).