Lack of seasonal variations in fertilization, pregnancy and implantation rates in women undergoing IVF.

BACKGROUND Several studies have investigated seasonal variations during IVF. Their results are contradictory, especially concerning fertilization and pregnancy rates. The aim of the present study was to re-evaluate these parameters using a large number of IVF cycles. METHODS A total of 7368 IVF cycles conducted in Switzerland between 1995 and 2003 were retrospectively analysed. To avoid a bias in the evaluation of the fertilization rate, only IVF cycles without ICSI were considered for analysis. Cycles were assigned to seasons according to the date of the beginning of stimulation. RESULTS There were no statistically significant differences between the seasons concerning the fertilization, the pregnancy and the implantation rates. However, statistically significant variables deciding on the outcome of an IVF cycle are age, centre, aetiology of infertility and day of transfer. CONCLUSIONS There were no statistically significant seasonal differences in central Europe (Switzerland) that influenced the outcome of IVF treatment. The only statistically significant variables of IVF outcome were age, centre, aetiology of infertility and day of transfer. A change to routine fertility treatment concerning the different seasons should therefore not be taken into account.