Seasonal influences on in vitro fertilization and embryo transfer.

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: 8184 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 pickups 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.