A team from Ben-Gurion University of the Negev in Beer-Sheva uncovered the seasonal pattern when they analysed samples taken from more than 6,000 men who had been treated for infertility and discovered that the sperm produced in winter and early spring was more abundant, had faster swimming speeds and fewer abnormalities. They detected that, as the seasons progressed, sperm steadily declined in quality.
The research team, reporting in the American Journal of Obstetrics and Gynaecology, said their findings could explain why there are more babies born during autumn than at any other time of year. Their findings could also be crucial in helping couples who have problems conceiving naturally and have sought fertility treatments.
The study revealed that the healthiest sperm was produced in winter among men whose sperm production was considered normal. On average those men produced about 70 million sperm per millilitre in winter with around 5% having “fast motility” to aid conception. This compared to 68 million sperm per ml later in the year when only 3% were fast.
Men whose sperm counts were considered abnormal or low did not show the same pattern. Their sperm motility was better during autumn with sperm counts higher during spring.
The study recommends that men with normal sperm counts who are struggling to conceive with a partner should concentrate their efforts in winter, while men with an abnormal sperm count should focus on autumn and spring.
Studies into animal reproduction have revealed similar patterns, which are explained by temperature changes and hormone changes but there has been no research to date into such patterns in humans.