A Danish travel company is calling for citizens of the country to step up to the mark with a tongue-in-cheek advert aimed at tackling the country's low birth rates.

Spies Rejser travel have launched the Do it for Denmark campaign, promising a child-friendly holiday and three years' worth of baby supplies for the winning couple who can prove they conceived their child while on one of their holidays.

The company says the advert is addressing the issue of low birth rates by asking Danes to "do it for Denmark" and have more sex.

The advert reads: "But if doing it for Denmark isn't motivation enough, we made a little competition. Book your holiday with your ovulation discount, get it on, and prove you conceived a child to win a three-year supply of baby stuff and a child-friendly holiday.

"But what if you already did your duty? Or what if your chance of conceiving a child isn't so high?

"Well look at it this way. It's not jut about winning. All the fun is in the participation."

The competition even provides useful tips for increasing fertility. It advises Danes to "take advantage of gravity" and "lie down for at least 15 minutes after sex," while advising men to avoid wearing tight clothing "even if you think it looks good".

In February 2013, a report described the birth rate among Danish women as "dangerously low" after it found over one in five couples were childless, despite most couples stating they wanted two or three children. The Copenhagen Post said the birth rate was approaching an "epidemic".

According to the report from the Copenhagen hospital Rigshospitalet, many couples are waiting longer to have children and there are less women of child-bearing age. This has led to concerns that there will not be enough people to support an aging population.

The Spies campaign states that 10% of all Danes are conceived on holiday - although this figure is unconfirmed.

The advert features a sex therapist, who explains that couples are more inclined to have sex while on holiday because their desire for each other increases.

Jan Vendelbo, the managing director of Spies, said they wanted to make reproducing "even more fun" by offering discounts on city breaks "to help with population growth".

The terms and conditions state that entrants are then sent a pregnancy tester kit after the holiday. If the result is positive, they are asked to send in a picture of the tester to Spies as proof of their conception.