['The efficacy of growth hormone (GH) co-treatment within a GnRH agonist long regimen, in women with a normal ovarian response to controlled ovarian hyperstimulation (COH), for IVF was assessed.', 'This retrospective clinical trial was performed in a private-assisted reproduction centre. The study involved 1114 patients who responded normally to high-dose gonadotropin treatment. The study group of 556 patients was given in a daily subcutaneous injection of 4.5\xa0IU of GH co-treatment, starting from the initial day of gonadotropin treatment and lasting for 5\xa0days. The control group of 558 patients received the same treatment protocol without the GH co-treatment. The participants were further divided into two subgroups: age ≥35\xa0years and age <35\xa0years. The primary endpoint of the study was IVF-ET outcomes.', 'The demographic characteristics did not significantly differ between the groups. The implantation rate (36.7 vs. 20.4\xa0%, P\xa0<\xa00.05) and clinical pregnancy rate (57.3 vs. 30.1\xa0%, P\xa0<\xa00.05) were significantly higher in the study group than in the control group. An analysis using a multivariate logistic regression model showed that GH was a significant factor for predicting pregnancy outcomes (OR 3.125, 95\xa0% CI 2.441-4.000). Furthermore, for the ≥35-year-old group, the endometrial thickness was significantly greater (11.99\xa0±\xa02.21 vs. 11.62\xa0±\xa02.45, P\xa0<\xa00.05) in the study group than in the control group; in contrast, for the <35-year-old group, the high-quality embryo rate was significantly higher (71.7 vs. 68.3\xa0%, P\xa0<\xa00.05) in the study group than in the control group.'] Does growth hormone co-treatment within a GnRH agonist long protocol improve implantation and pregnancy rates in patients undergoing IVF-ET?