Here it is, your ticket to fatherhood. We beg of you though, stay away from satin.

For men trying to start a family, it's time to lose the tight jeans - and sleep naked.

Underwear choice has a huge impact on a man's sperm count and quality, according to research from Stanford University, the Daily Mail reports.

Their findings? Breezy boxer shorts keep reproductive cells alive, while sleeping in your birthday suit gives the best results.

Stanford scientists worked with the US National Institute of Child Health and Human Development on a sample of 501 men who were trying to become fathers.

Those who wore boxer shorts during the day, rather than tighter briefs, and wore nothing at all to bed, had 25 per cent less damage to their sperm.

Katherine Sapra of the NICHD said there was an association between the type of underwear worn, and semen quality.

"Reducing exposure for bed decreases DNA fragmentation; better semen quality parameters are observed in men wearing boxers during the day and none to bed."

Allan Pacey of Sheffield University agreed, saying heat was the factor at play.

"We have known for some time that men who increase the temperature of their testicles, either through the heat exposure at work or by wearing tight underwear, have poorer semen quality compared to men whose testicles are cooler," he said.

'Switching underwear is hardly a risky thing to do, so buying some looser pants might be good advice for would be fathers."