Statistical analysis of factors affecting fertilization rates and clinical outcome associated with intracytoplasmic sperm injection

Objective: To identify and evaluate the statistically significant predictors of intracytoplasmic sperm injection (ICSI) fertilization rates and clinical pregnancy in a single population using appropriate statistical techniques. Design: Retrospective study. Setting: Fertility and Endocrinology Center, University of Washington Medical Center, Seattle, Washington. Patient(s): Four hundred forty-one patients undergoing their first attempt at IVF-ICSI from January 1, 1999, to May 21, 2001. Intervention(s): Each ICSI procedure for an individual patient was performed by a single operator. Sperm parameters, oocyte age, culture condition, ICSI technique, and ICSI operator were assessed as variables influencing the fertilization rate. We also assessed the impact of patient age, serum E₂ concentration on the day of hCG administration, embryo quality, and number of embryos transferred on the probability of achieving a clinical pregnancy. Main outcome measure(s): Fertilization rate and clinical pregnancy. Result(s): The 2 pronuclei (2PN) rate was significantly correlated with sperm motility, and there were significant differences in the 2PN rates among the ICSI operators. There was no difference in the 2PN rate among different sperm types or among the eight laboratory incubators or whether the eggs were cultured individually or in groups. Patient age, serum E₂ concentration on the day of hCG administration, embryo quality, and number of embryos transferred were all statistically significant predictors of clinical pregnancy. Conclusion(s): In our program, sperm motility and ICSI operator are the two most important predictors for the ICSI fertilization rate in vitro. Patient age, serum E₂ concentration on the day of hCG administration, embryo quality, and number of embryos transferred were all statistically significant predictors of clinical pregnancy.