Exogenous influences on human fertility: fluctuations in sperm parameters and results of in-vitro fertilization coincide with conceptions in the normal population.

Intra- and interindividual short-term fluctuations of sperm parameters were observed in assisted reproduction patients, paralleled by respective fluctuations of the in-vitro fertilization (IVF) results. To test whether the fertility fluctuations observed in the clinic were representative for the overall population, birth statistics of two normal subpopulations (urban and rural) were studied. There were highly significant parallels in the fluctuations of the monthly deliveries in both normal subpopulations. Also, there was a significant correlation when the fluctuation of sperm parameters in IVF patients was compared with those of a control group. Furthermore, delivery fluctuations in the overall population were significantly paralleled by fluctuations in sperm parameters and IVF results around the conception time of these deliveries. In all groups, the pattern and amplitude of the short-term fluctuations varied from year to year. Frequently observed peaks in late autumn gave rise to the appearance of a semi-seasonal variation in fertility. The existence of an external influence on overall male gamete quality must be postulated, which has considerable influence on the IVF results. This short-term influence might be causally linked to the factors responsible for the previously found annual variation in human fertility and possibly for the long-term changes in human reproductive function.