Analysis of donor heterogeneity as a factor affecting the clinical outcome of oocyte donation.

This study investigated factors that may affect the clinical outcome of oocyte donation on the basis of data from a clinical programme involving 243 treatment cycles analysed retrospectively. In each cohort, oocytes were distributed randomly to one, two or three recipients, which enabled the outcomes in terms of pregnancy and live birth rates to be compared among donors. The results were compared with respect to age of the donor and recipient, number of oocytes collected, fertilization and cleavage rates, qualitative embryo criteria (morphological grade) and other clinical criteria. Most variables had no significant effect on either outcome, although the live birth rate varied inversely with recipient age. Unsurprisingly, the pregnancy rate was correlated positively with the number of embryos transferred. Most of the variation in pregnancy and live birth rates (85-90%) could not be accounted for by any specific donation characteristic, indicating that interdonor heterogeneity was the result of idiopathic factors. The factor most predictive of a recipient's cycle outcome was a history of previous success of the donor, which accounted for approximately 30% of the variation in live birth rates. Pregnancy success rates varied widely among oocyte donors, as has been found among sperm donors. This observation highlights the need to identify markers that predict developmental competence and help to identify the genetic and environmental bases of differential fertility. In conclusion, the quality of oocytes varied widely among women presumed to be fertile by clinical criteria, and the causative factors set a major limitation on the prospects of improving the outcome of egg donation.