Sperm get spring fever, too – but they're especially frisky in winter, a new study has found.
The data show that couples don't conceive the most babies in winter just because there's nothing else to do, Reuters reports.
Sperm produced in winter and early spring swim faster, in greater numbers and with fewer abnormalities, according to a recent Israeli study published in the American Journal of Obstetrics and Gynecology.
By contrast, sperm numbers and mobility "showed a significant decrease from spring toward summer and fall," observed the researchers, who analyzed 6,455 sperm samples from men at a fertility clinic over a three-and-a-half-year period, from January, 2006, to July, 2009.
"The winter and spring semen patterns are compatible with increased [fecundity] and may be a plausible explanation of the peak number of deliveries during the fall," wrote lead researcher Eliahu Levitas from Ben-Gurion University of the Negev in Beer-Sheva.
But according to Statistics Canada, July to October are the peak months for Canadian births, which means a great deal were conceived in October and November, not winter or spring. The study has an explanation for that too. The seasonality of good sperm depends on a man's baseline fertility, the researchers found.
Of the 6,455 sperm samples collected, 4,960 were considered to be normal, whereas 1,495 were found to show abnormal production, such as low sperm counts.
Two-thirds of the men had normal sperm production, defined as at least 16 million sperm for each millilitre of semen. In winter, they produced the most sperm – 70 million sperm a millilitre – and a higher percentage of fast swimmers.
Men with abnormal sperm production, however, were slightly more likely to make fast swimmers in the fall and a larger percentage of healthy sperm during the spring.
"Based on our results the [normal] semen will perform better in winter, whereas [couples with infertility] related to low sperm counts should be encouraged to choose spring and fall," the researchers wrote.
For aspiring parents, of course, there's no time like the present.