Purpose: The study was aimed to investigate the influence of time factors (day, week, month) on pregnancy rates and in vitro fertilization (IVF) and embryo transfer (ET) parameters.
Methods: 8,184 IVF-ET cycles, taking place in two IVF centers from 1992 to 1999, were analyzed. Multiple logistic and linear regression methods were performed as statistical analyses.
Results: Oocyte pickup on Tuesdays achieved a significantly higher mean number of oocytes (median: 7) and the highest pregnancy rate (PR) (33.4%) per ET There was a significant variation over the year, with the lowest PR/ET in July (25.71%) and the highest in December (35.5%). Concerning outcomes, the age factor and the number of embryos transferred had the highest significant (p < 0.0001) influence.
Conclusions: The observed weekly rhythm for oocyte pick-ups is certainly due to preprogrammed ovarian stimulation used in our IVF programs. Age as well as the number of embryos transferred are the main influencing factors on a positive outcome and more predictive than seasonal aspects.