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

The purpose of this study was to determine whether there isa seasonal variation in implantation and pregnancy rates followingnatural cycle replacement of cryopreserved embryos. A totalof 321 consecutive cycles were analysed. There were 59 pregnancies(18.4%) and 48 live births or ongoing pregnancies (15.0%). Indicatorvariables for each month and variables representing temporalcycles 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 topregnancy. This study indicated that there was no clear seasonalvariation in the pregnancy rate following natural cycle replacement.However, the power of this study was low, and it was estimatedthat 963 subjects would be required to detect a 10% seasonaldifference in pregnancy rates.