Successful pregnancy outcome after cryopreservation of all fresh embryos with subsequent transfer into an unstimulated cycle

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To assess the pregnancy outcome of freezing and storing all fresh embryos produced in a stimulated IVF cycle and replacing them in a subsequent nongonadotropin-stimulated cycle. Retrospective study. University-associated assisted reproductive technology program. We studied 36 patients (age range 23 to 44 years) who underwent cryopreservation of all fresh embryos in a controlled ovarian hyperstimulation (COH) cycle because of either the risk of severe ovarian hyperstimulation (24 patients, group 1) or the presence of an endometrial lining < 8 mm in thickness (12 patients, group 2). Five hundred fifty-five embryos were generated for replacement in 63 cycles. All embryos were cryopreserved in 1.5 M propanediol at the pronuclear or two-cell stage, and 264 embryos subsequently were transferred into a hormone replacement cycle (70%) or natural ovulatory cycle (30%). The average number of embryos transferred per patient was 4.2. Twenty-one clinical pregnancies were achieved, giving a pregnancy rate (PR) of 58.3% per patient (33.3% per cycle). The live birth rate was 50% per patient (28.6% per cycle). The implantation rate was 9.1%. Groups 1 and 2 had a similar PR per patient (58.3%). With 208 cryopreserved embryos remaining and considering the 33.3% PR per cycle, we expect the overall extrapolated PR to be 63.9%. This is the first series showing that freezing and storing all fresh embryos produced in a stimulated IVF cycle and replacing them in a subsequent nongonadotropin-stimulated cycle results in successful PRs. These results underlie the importance of a successful cryopreservation program in IVF and could be a possible approach to overcoming the alleged adverse effects of COH on the endometrium, thereby improving the chances of pregnancy when numerous embryos are obtained simultaneously.