Multiple factors have been attributed to affect the outcome of IVF pregnancies achieved through oocyte donation; some of them include embryo quality, endometrial receptivity, reproductive status of the recipient, and the ages of the donor and recipient. Despite contradictory evidences on the effect of the recipient’s age, the age of the donor has been identified as a significant factor influencing the outcomes of assisted reproduction. Results of a multivariate analysis published in the journal Fertility and Sterility has further substantiated the crucial association between the donor’s age and the number of mature oocytes/embryos obtained. The study results also proposed the significance of other factors, such as estradiol level on the day of hCG administration and amount of gonadotropin used in the stimulation protocol, for predicting IVF outcome.
The retrospective cohort study performed by Sara E Barton from the Brigham and Women’s Hospital, Massachusetts, and colleagues, evaluated the independent associations of oocyte donor follicle stimulating hormone (FSH) levels and age with IVF outcome. The main outcome measures included the number of mature oocytes and embryos obtained from donors, and clinical pregnancy and live birth rates associated with the cycles. The study conducted on 312 donor-recipient pairs opting for oocyte donation IVF, reported the following results:
• For every one-year increase in the donor’s age, the corresponding decrease in the number of mature oocytes and embryos was 0.39 and 0.25, respectively. This in turn resulted in the depletion of one embryo for every four-year advancement in the donor’s age. Similar findings were observed even in the case of young donors
• No significant association was noted between the donor’s basal FSH levels and IVF success
• On the day of hCG administration, the number of mature oocytes and embryos increased by 0.49 and 0.36, respectively, with every 100 pg/mL increase in estradiol concentration
• The probability of pregnancy and live birth was reduced by 3.5% for every additional 75 IU increase in gonadotropin indicated for ovarian stimulation
In an effort to optimize the IVF treatment outcome, researchers have assessed various factors of egg donors that could affect pregnancy in recipients, through assisted conception. An earlier study (Human Reproduction, 1999), also demonstrating the significance of donor’s age, ruled out the need for considering parity in the selection of candidates for oocyte donation. In the study, Cohen et al also concluded that the total number of retrieved oocytes is insignificant for predicting the outcome.
Another recent study by Garcia-Cruz et al (Human Reproduction, 2009) concluded that aneuploidy frequency in donor oocytes can be considered as an important factor that could influence the outcome of oocyte donation-based IVF cycles. In contrast to studies suggesting the association of aneuploidy with increased donor age, the study demonstrated a considerable occurrence of aneuploidy in oocytes obtained from younger donors (18 to 35 years old). Also, the researchers observed highly defective patterns of meiotic recombination in chromosome 16 that could result in a chromosomal non-disjunction, thereby increasing the risk for conceiving a trisomic 16 embryo.
The American Society for Reproductive Medicine (ASRM) has recommended the preferred age for oocyte donors to be between 21 and 34. The organization also cautioned regarding the enhanced risk of aneuploid offspring while using oocytes obtained from donors ≥35 years of age. However, there is a lack of strict consensus on the need for performing aneuploidy screening in this age group.
References
1. Barton SE, Missmer SA, Ashby RK, Ginsburg ES. Multivariate analysis of the association between oocyte donor characteristics, including basal follicle stimulating hormone (FSH) and age, and IVF cycle outcomes. Fertil Steril. 2009 Oct 12. [Epub ahead of print]
2. Cohen MA, Lindheim SR, Sauer MV. Donor age is paramount to success in oocyte donation. Hum Reprod. 1999 Nov;14(11):2755-8.
3. Garcia-Cruz R, Casanovas A, Brieño-Enríquez M, et al. Cytogenetic analyses of human oocytes provide new data on non-disjunction mechanisms and the origin of trisomy 16. Hum Reprod. 2009 Oct 14. [Epub ahead of print]
