Seasonality and human in vitro fertilization outcome.

Seasonal changes in spontaneous fecundity have been observed in several human populations, but it is not clear whether the same applies to human in vitro fertilization-embryo transfer (IVF) procedures. In the present study, 2067 patients undergoing their first IVF attempt between the years 1998 and 2003 were grouped into four 'seasons' (December-February, March-May, June-August, September-November) according to the day on which they were administered human chorionic gonadotropin. Several parameters known to affect IVF outcome (including ovarian response to gonadotropins, sperm and oocyte quality, fertilization rate, embryo quality, pregnancy and implantation rates) were considered and potential changes among the four seasonal periods were analyzed. Moreover, some confounding variables (sperm quality, age, duration of infertility, indications for IVF) were controlled for. Overall, pregnancy rate per oocyte pick-up and per embryo transfer of 32.5% and 35.8%, respectively, as well as implantation rate of 18.9%, were recorded. None of the observed IVF-related parameters showed any significant change clearly related to a specific seasonal period, their fluctuations throughout the year being randomly determined. Ovarian responsiveness to gonadotropins, quality of gametes and embryos, and fertilization and implantation processes were apparently not significantly affected by seasonality. It is concluded that the results of a good-quality IVF program in humans are not significantly affected by the season of the year in which the IVF attempt is accomplished; therefore, season is not a relevant factor to be considered when planning an IVF treatment.