Outcomes of different times of vitrification-thawed embryo transfer in freeze-all cycles paitents

Objective To explore the clinical outcomes of different times of frozen embryo transfer (FET) cycles in the freeze-all cycles. Methods A total of 807 patients who underwent all embryos cryopreservation between January 2012 and September 2016 were analyzed. According to the different times of FET cycles in the same oocyte retrieval, they were divided into 4 groups: patients underwent FET once as group A (n=543), twice FET as group B (n=181), three times FET as group C (n=63), and four times FET as group D (n=20). The clinical medical records of two groups were retrospectively analyzed. The general clinical data, transfer cycles and the rates of cumulative pregnancy and clinical pregnancy among 4 groups were analyzed. Results ①There was no statistically difference with four groups in general characteristics which includes age, duration of infertility, infertility type, body mass index (BMI), basic follicle stimulating hormone (FSH) levels, basic luteinizing hormone(LH)levels, basic estradiol levels, basic testosterone levels, optimum number of oocytes, number of metaphase Ⅱ(MⅡ) oocytes, normal fertilization rate, number of available embryos(P>0.05). ②There was no statistically difference with four groups′clinical data including endometrial thickness, embryo number transferred, prime embryo rate and artificial cycle rate for endometrial preparation program (P>0.05). ③The cumulative pregnancy rates per collection cycle of 4 groups were 64.5%, 60.0%, 58.7% and 60.0%, respectively. And there was no significant difference (χ2=1.67, P=0.64). The clinical pregnancy rates were 64.5%, 36.5%, 25.1% and 18.8%, respectively. And there was significant difference(χ2=143.02, P<0.01). Conclusions The increasing of the number of FET transplantation in the same oocyte retrieval were not increased the total pregnancy rate of freeze-all cycles, but decreased the clinical pregnancy rate. Key words: Cryopreservation; Embryo transfer; Oocyte; Pregnancy rate; Women