Couples who have fertility problems due to low-quality sperm would be well advised to plan their calendars: Soroka University Medical Center researchers have found that the quality of semen – both the amount of sperm and their motility – is better in the winter and the fall than in the spring or summer.Dr. Eliahu Levitas, a senior physician in the hospital’s in-vitro fertilization unit, reported to a recent meeting of the Israel Society for Fertility Research about his statistical study of 6,453 semen samples collected at Soroka.He found that in the spring, there begins a decline in the concentration of sperm in the semen as well as their ability to impregnate ova. The decline continues through the summer and continues into the autumn months.Not only the small concentration of sperm in the semen can reduce the chances of a pregnancy but also how well the sperm, with their tiny tails, are able to swim toward the egg. This motility is best in winter. In addition, more sperm cells were found to be normal compared to defective ones that were produced during the warmer months.Levitas said that the heat in the scrotum, which lies outside the body, hurts sperm quality and concentration. It is known, he said, that truck drivers who sit much of the day, as well as bike riders whose scrotums heat up from friction of pedaling, have lower fertility than others. In addition, men who wear tight jeans also have a higher risk of such problems.