A retrospective analysis of factors influencing oocyte degeneration post-ICSI

Abstract

Objective: To understand better why some oocytes degenerate after ICSI, we investigated potential correlations between oocyte degeneration rates and: a) patient age; b) day 3 FSH; c) days of ovarian stimulation; d) type of stimulation; e) estradiol (E2) level on day of hCG administration; f) number of oocytes retrieved; g) oocyte maturity at time of cumulus stripping and ICSI; and h) the interval between oocyte retrieval, cumulus stripping, and ICSI. We hypothesized that increased degeneration rates would correlate to poorer prognosis indicators such as, increased patient age, elevated day 3 FSH, and lower E2 levels. Design: A retrospective analysis. Materials and Methods: Data were collected from all ICSI cases during the last six months of 2002 (497 cases, 4933 injected oocytes), analysis was conducted between oocyte degeneration and the previously mentioned variables. Correlations were evaluated non-parametrically using Spearman’s Rho due to the highly non-normal distribution of oocyte degeneration rates. Stepwise multiple regression analysis of ranked data values was used to model the influence of multiple independent variables on oocyte degeneration rates. Results: The percentage of oocyte degeneration after ICSI was significantly correlated to four of the analyzed variables: a younger patient age (Rho = −0.098, P = 0.028); a higher E2 level on day of hCG (Rho = 0.106, P = 0.018); a larger number of oocytes injected (Rho = 0.151, P = 0.0007); a longer period between oocyte retrieval and ICSI (Rho = 0.127, P = 0.0045). The number of injected oocytes was also correlated with each of the other three variables (Rho = −0.242, p < 0.0001 for age, Rho = 0.646, P < 0.0001 for E2 level, and Rho = 0.183, P < 0.0001 for period between retrieval and ICSI). Stepwise multiple regression analysis indicated that oocyte degeneration rates were significantly influenced both by the number of oocytes injected (P = 0.0035), and by the interval between retrieval and ICSI (P = 0.022), but not by age (P = 0.152) or E2 level (P = 0.77). Conclusion: Contrary to our expectations, the strongest correlation observed suggested that cases with more oocytes for injection are more likely to have a higher rate of degeneration. On the other hand, it was not surprising to find that a longer duration in vitro prior to ICSI negatively affected oocyte survival. The negative correlation between age and oocyte degeneration, and the positive correlation between E2 level and oocyte degeneration appear to be indirect results of relatively strong correlations between both age and E2 level, and the number of mature oocytes.