Objective: IVF-ET provides unique controlled conditions for the study of seasonal influences on the human reproductive process. This study was designed to evaluate the effects of seasonality on fertilization rate, embryo quality, and conception rates.
Design: A retrospective observational cohort study. A chart review of all individuals undergoing IVF-ET from 1988 to 1991 at our institution was performed.
Setting: An assisted reproduction unit at a university-based tertiary medical center.
Patient(s): 657 women, for a total of 1074 IVF-ET treatment cycles, were evaluated. From this population, we chose 305 women undergoing their first IVF-ET cycle for reasons of pure mechanical infertility.
Intervention(s): IVF-ET cycles.
Main outcome measure(s): Seasonal variability in fertilization rates and quality-A embryo rates, and the correlation with the absolute number of light hours, as well as the influence of temperature, humidity, and other environmental parameters.
Result(s): A significant seasonal variability in the fertilization rate and the quality-A embryo rate was demonstrated. The highest fertilization and quality-A embryo rates were observed during the spring and the lowest in the autumn. These changes correlated with the absolute number of light hours and its increment over time, but not with the temperature, humidity, or other environmental parameters.
Conclusion(s): Seasonality seems to have a significant influence on the fertilization process and on the quality of the human embryos that are obtained in vitro, possibly because of the light/dark variations over time. If this finding is confirmed, these seasonal changes should be taken into account when evaluating infertility data and in everyday clinical practice.