Background: The goal of this study was to examine the impact of body mass index (BMI) and age on the outcome of the IVF process.
Materials and methods: This was a retrospective case-control study, of all patients undergoing IVF from 2008-2010 in the Re-Medika IVF Centre. A total of 1238 fresh, non-donor IVF cycles were analyzed, but to minimize the bias, only the first cycle for each patient in that period was analysed (N-920). The patients underwent standard protocols for COH and embryology treatment. In all retrieved oocytes, or in 100% of the cases, the process of fertilization was realized with the method of intracytoplasmic sperm insemination (ICSI). The primary end-point assessed was clinical pregnancy rate. Patients were initially grouped into four BMI categories. The data are presented as frequencies (qualitative data) and as mean±SD (quantitative data). Preliminary comparisons between groups with different BMI were made by the Chi-square and one-way ANOVA test. Because fertility declines with age, there is a Pearson-correlation coefficient to see if BMI depends on age, and the resulting value r=0.15 (p<0.05) showed that BMI is age-dependent, the relationship between them showed multicollinearity. However, the calculated error tolerance of 0.9 indicates stability of the model. Furthermore, to adjust the known fertility decline with age, every response or outcome is analysed by the method of multiple linear (continuous data) or logistic (qualitative data) regression, where the independent variables are taken: BMI, age and BMI interaction×age.
Results: Increased BMI significantly reduces the chance of clinical pregnancy (normal weight vs. overweight: clinical pregnancy rate: 49.2%, vs. 34.3%). Age, analysed as a single factor, significantly reduces clinical pregnancy rate. Interaction of BMI and age significantly affects clinical pregnancy rate. (BMI vs. BMI×Age vs. Age-p 0,01 vs. 0,001 vs. <0,0001).
Conclusion: Increased body mass of patients entering IVF has a negative impact on the final outcome and certainly reduces the success of the process resulting in reduced clinical pregnancy. Interaction of BMI and age showed a strong significant impact on the outcome of IVF seen through the achievement of clinical pregnancy.