Cryo-thawed embryos obtained from conception cycles have double the implantation and pregnancy potential of those from unsuccessful cycles

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Abstract
BACKGROUND: The purpose of this study was to evaluate the influence of fresh IVF/ICSI cycle outcome on the prognosis of the related frozen embryo replacement (FER) cycle. METHODS: 459 FER cycles, involving 2049 cleavage stage embryos with no or up to 10% fragmentation, were performed for which the outcome of the fresh cycle was recorded. The cycles were divided into two groups; group A included cycles in which cryopreserved embryos were obtained from fresh cycles in which conception occurred. Group B were cycles in which cryopreserved embryos originated from unsuccessful fresh cycles. RESULTS: Groups A and B were comparable with respect to mean (± SD) age at cryopreservation (33 ± 3.9 versus 33.2 ± 4 years, P = not significant), mean number of oocytes retrieved and fertilized normally in the fresh cycle (11 ± 5.2 versus 11.2 ± 4.8, P = not significant) and mean age at the cryo‐thawed transfer (34.5 ± 4.2 versus 33.9 ± 4 years, P = not significant). No significant difference was found between the two groups with regard to mean number of embryos cryopreserved (6.5 ± 3.9 versus 6.2 ± 3.6) and subsequently thawed (4.5 ± 2.5 versus 4.5 ± 1.8) per cycle and number of cryo‐thawed embryos transferred per cycle (2.0 ± 0.7 versus 2.1 ± 0.8). However, the implantation rate per transferred embryo in group A was double that in group B (23 versus 11.2%, P < 0.0001). Moreover, the clinical pregnancy and ongoing pregnancy rates per cycle were significantly higher in group A compared with group B (34.8 and 27.3% versus 15.6 and 13.1%, P < 0.0001 and P = 0.0003 respectively). The difference in FER cycle outcome could not be explained by confounding variables. CONCLUSIONS: After thawing, cryopreserved embryos originating from conception IVF/ICSI cycles achieve double the implantation and pregnancy rates of those obtained from unsuccessful cycles.

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