Human embryo implantation following in-vitro fertilization: is there a seasonal variation?

The purpose of this study was to determine whether there is a seasonal variation in implantation and pregnancy rates following natural cycle replacement of cryopreserved embryos. A total of 321 consecutive cycles were analysed. There were 59 pregnancies (18.4%) and 48 live births or ongoing pregnancies (15.0%). Indicator variables for each month and variables representing temporal cycles of 12, 6, 4, 3 and 2 months were related to outcome. In addition, an analysis of periodicity was performed. No temporal, clinical or demographic variable was significantly related to pregnancy. This study indicated that there was no clear seasonal variation in the pregnancy rate following natural cycle replacement. However, the power of this study was low, and it was estimated that 963 subjects would be required to detect a 10% seasonal difference in pregnancy rates.