Frozen-thawed embryo transfer is better than fresh embryo transfer in GnRH antagonist cycle in women with 3-10 oocytes retrieved: a retrospective cohort study

Purpose To compare the clinical outcome of fresh embryo transfer with frozen-thawed embryo transfer in subsequent cycle of GnRH antagonist protocol. Methods Totally, 1430 women were enrolled from the cases of our Assisted Reproduction Center from January 2015 to January 2019 for this retrospective cohort study. The inclusion criteria of the subjects included women with ages under 40 years, 3-10 oocytes retrieved, good embryo quality according to gardener score, GnRH antagonist protocol, underwent first cycle of fresh embryo transfer or freeze-all strategy and transferred in subsequent cycle. However, the patients with endometriosis, PGD/PGS cycles, history of recurrent pregnancy loss and uterine pathology were excluded. 495 women of group I underwent fresh embryo transfer in first cycle and 935 patients of group II received frozen-thawed transfer in subsequent cycle. The primary outcome was clinical pregnancy rate. A logistic regression analysis was performed to determine the variables that could be independently associated with clinical pregnancy rate. Models were adjusted for covariates including patients' age, fertilization type, infertility type, infertility duration, the number of oocytes retrieved, the number of embryos transferred and type of embryo transferred. Results Clinical pregnancy rate was significantly higher in frozen-thawed embryo transfer than in fresh embryo transfer (63.70% vs. 54.50%, p < 0.001). Miscarriage rate and ectopic pregnancy rate were comparable between two groups. Variables independently associated with clinical pregnancy rate were fresh/frozen embryo transfer, patients' age and the number of embryos transferred. After adjusting for variables, the frozen embryo transfer [adjusted odds ratio (aOR) 0.75; 95% CI, 0.59-0.95, p = 0.016] was a predictive factor of clinical pregnancy rate. Conclusion Frozen embryo transfer is better than fresh embryo transfer in GnRH antagonist cycle in women with 3-10 oocytes retrieved.