The research, presented at the American Society for Reproductive Medicine annual conference in Denver, looked at sperm samples taken from 29000 men over 17 years and compared the sperm quality to the time of year the samples were taken.It found that the total motile sperm count – the number of moving sperm – was highest in the spring but the number of normal shaped sperm was highest in the autumn.Dr Nazem added: “Maybe autumn and spring are just a little bit more balanced, the temperatures are a more mild and people are still out and about and more physically active than in the winter.“They could still be eating healthily from the summer. There’s something about these in-between seasons when people are preparing or recovering from the two extremes of winter and summer.“Men should evaluate their lifestyle habits in these seasons, especially diet and exercise, and attempt to maintain a similar lifestyle throughout the year.”In the summer, men had an average of 112 million moving sperm per millilitre, down from 117 million in spring, the study showed.Allan Pacey, professor of andrology at the University of Sheffield, said: “We’ve known for a while that sperm quality can change with season, although the exact differences vary from study to study. “This is certainly the biggest study I am aware of, and confirms that sperm quality is at its worst in the summer months.“It might make a small difference to the chances of pregnancy, although more research is needed.” Men produce the strongest sperm in spring and autumn, according to the largest study of its kind.Experts think sperm health may be linked to the number of hours of daylight during these months and the fact men do more exercise than during the cold winter.Men are also likely to drink less than at Christmas or when they go on a summer holiday. The mild spring and autumn temperatures could also help sperm stay cooler, which prevents damage, they said.However, the fact that it takes three months for the body to produce sperm has meant experts are still unsure of exactly what environmental factors may have caused the shift.And they say it is too soon to know if this could affect the chance of pregnancy.A study from the Icahn School of Medicine in Mount Sinai, New York concluded that the time of year does affect sperm.Lead author Dr Taraneh Nazem, from Icahn School of Medicine, said: “In this very large retrospective study we found semen quality is higher in the autumn and spring.“It is possible that male fertility is better in these seasons but further research is needed to know how these findings affect pregnancy success rates. “However it is something to take into consideration and doctors could discuss these seasonal changes with men.” Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.