Investigating effective factors on intra cytoplasmic sperm injection embryo quality using the marginal and generalized additive statistical models

In vitro fertilization techniques are used for many years. In such methods, if feasible, it is always better to transform a high quality embryo into uterus to enhance the chance of the success. Therefore, a comprehensive research was conducted to identify important factors related to the embryo quality. We considered potential correlation between embryos derived from an infertile couple in our statistical analyses. In addition, possible nonlinear relationships between the factors and the embryo quality were investigated. In this study, after collecting the necessary information, the statistical method of generalized additive models (GAM) has been employed to determine any nonlinear relationship between quantitative exploratory variables and the response. Then, the results were used to analyze the data using the Generalized Estimating Equation (GEE) technique. Such model can handle correlation which may present among infertile couple embryos. Finally, important factors related to the embryo quality of in-vitro fertilization by intra-cytoplasmic sperm injection methods were identified. Based on results of the GEE, linear relationships of drugs, type of infertility, and polycystic ovary syndrome was statistically significant on embryo quality. Interestingly, after examining the nonlinear relationships with GAM, in addition to the above variables, smoking status, sperm motility, and uterine factor were also shown to be significant. Since observations on a single subject in fertilization techniques are correlated and the relationship between factors and outcomes of fertilization may not be linear, the usual methods of GAM should incorporate the potential intra-cluster correlation using models such as the GEE. Our results suggest significant effects of tobacco use, drugs, polycystic ovarian syndrome, type of infertility, and sperm motility on the embryo quality. Sperm motility has non-linear effect on embryo quality resulting from in vitro fertilization and improved the overall model fit.