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 IU of GH co-treatment, starting from the initial day of gonadotropin treatment and lasting for 5 days. 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 aeyen35 years and age < 35 years. 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 %, P < 0.05) and clinical pregnancy rate (57.3 vs. 30.1 %, P < 0.05) 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 % CI 2.441-4.000). Furthermore, for the aeyen35-year-old group, the endometrial thickness was significantly greater (11.99 +/- A 2.21 vs. 11.62 +/- A 2.45, P < 0.05) 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 %, P < 0.05) in the study group than in the control group. Our study showed that co-treatment with GH in a GnRH agonist long protocol in patients who responded normally while undergoing IVF-ET could increase the implantation and pregnancy rates.