Gestational surrogacy enhances implantation rates in egg donation cycles

Abstract

Objective: Evidence derived from egg donation studies suggests that oocyte quality may be the most important factor determining implantation failure and pregnancy loss. The potential role of a uterine factor, other than in cases with detectable uterine pathology, is more controversial. The aim of this study was to assess the contribution of a possible uterine factor on implantation and pregnancy loss by comparing embryo transfers into surrogate and non-surrogate recipients. By considering only egg donation cycles, the confounding effects of oocyte quality were controlled. Design: A retrospective analysis of IVF/ICSI fresh and frozen (FET) egg donation cases performed at one center over a five-year period, 1997–2002. Women with detectable uterine pathology were excluded. Materials and Methods: A total of 172 fresh cases (53 IVF and 43 ICSI non-surrogate, and 56 IVF and 20 ICSI surrogate) and 64 frozen transfers (37 non-surrogate and 27 surrogate) were evaluated. Surrogate and non-surrogate cycles were compared with respect to age of oocyte donor (for FET cycles, age when embryos were frozen), age of embryo recipient (surrogate/patient), number of embryos transferred, and implantation, clinical pregnancy and miscarriage rates using chi-square or unpaired t-tests, as appropriate, for statistical analysis. The same clinical protocol was used to prepare the endometrium in both surrogates and non-surrogate recipients. Results: There were no significant differences in the number of eggs retrieved, fertilization rate or number of embryos transferred between the surrogate and non-surrogate groups. Implantation rates following fresh embryo transfers were significantly higher for surrogates (42%) than for non-surrogates (33%, p<.05). Surrogates also had a higher implantation rate (28%) than non-surrogates (15%, p<.01) in FET cycles. Although there were no significant differences in clinical pregnancy rates between the surrogate (73%) and non-surrogate (65%) groups for fresh embryo transfer cycles, surrogates had a significantly higher pregnancy rate (74%) than non-surrogates (43%, p<.025) in FET cycles. There were no significant differences in miscarriage rates between the surrogate and non-surrogate groups. Conclusion: Implantation rates are enhanced in fresh and frozen egg donation cases using gestational surrogates as compared to non-surrogates. This increase in implantation rates in surrogates is seen in both male factor and non-male factor cases. This data suggests that, in addition to the previously reported effects of oocyte quality, a uterine factor may contribute to implantation failure, and it supports the use of a gestational surrogate for patients with repeated pregnancy failure using egg donation.