Human Reproduction, Vol. 18, No. 6, 1313-1318,
June 2003
© 2003 European Society of Human Reproduction and Embryology
Cryo-thawed embryos obtained from conception cycles have double the implantation and pregnancy potential of those from unsuccessful cycles
Assisted Conception Unit, Guy’s and St Thomas’ Hospital NHS Trust, St Thomas’ Street, London SE1 9RT, UK
1 To whom correspondence should be addressed. e-mail: tarekeltoukhy{at}hotmail.com
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.
Key words: cryo-thawed cycle prognosis/embryo cryopreservation/IVF outcome
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