Determinants of pregnancy rate in the donor oocyte model: a multivariate analysis of 450 frozen-thawed embryo transfers

Conflicting results have been published about the determinants of pregnancy after oocyte donation (OD). We used the OD model to determine predictive factors of pregnancy in the recipient after frozen-thawed embryo transfer (FTET) in a specific series where all the embryos were cryopreserved without any prior selection for fresh transfer. We report a retrospective study in a university tertiary care center. Multivariate analysis and logistic regression were used to identify predictive factors of pregnancy in a series of 450 OD FTET cycles in 198 infertile women between January 1992 and December 2006. The mean (+/- SD) recipient age was 35.7 (+/- 4.5). Impaired ovarian function was the main indication for OD. The mean +/- SD (range) number of embryos transferred was 1.65 +/- 0.5 (1-3). Overall clinical pregnancy, implantation and delivery rates were 30, 18 and 23%, respectively. After univariate analysis, pregnancy rates were significantly higher in recipients under 35 years, in women with a body mass index (BMI) < 30 kg/m(2), in women with an endometrial thickness of >= 8 mm, in amenorrheic women and in women not receiving pituitary down-regulation before endometrial preparation. Using multivariate analysis, the BMI, endometrial thickness and the use of pituitary down-regulation were independent predictors of pregnancy, regardless of age. This study supports that endometrial thickness of < 8 mm, obesity and the use of GnRH analogue pituitary down-regulation before endometrial priming negatively impact pregnancy rates, independently of the recipient's age.