- Objective To compare the different sperm parameters according to season of the year on sperm production day and the season 70 days prior (during spermatogenesis). Study Design Retrospective Andrology Laboratory data comparison. A total of 6455 consecutive semen samples were collected as part of the basic fertility evaluation of 6447 couples. According to sperm concentration, the samples were classified as Normozoospermic or Oligozoospermic and analyzed in relation to the season. Results The sperm concentration and percentage of fast motility showed a significant decrease from spring toward summer and fall (P < .001) with recovery noticed during the winter. As well, the highest percentage of normal sperm morphology was observed during the winter months. Conclusion Seasonal sperm pattern seems to be a circannual-rhythmic phenomenon. The winter and spring semen patterns are compatible with increased fecundability and may be a plausible explanation of the peak number of deliveries during the fall.