Sperm banks are trying to make donating seem masculine in a bid to draw men in, according to scientists.
In the UK and Australia clinics aren't allowed to pay men to donate sperm so may be trying to entice donors by depicting them as selfless or heroic.
Military-style recruitment posters, phrases like 'good men' and 'life changing', and comparisons with traditionally male jobs like firefighting have been used.
Researchers said they were 'surprised' clinics operated by calling potential donors' masculinity into question and said the same thing wasn't done to attract women.
Research by City, University of London, and Cardiff University studied advertising campaigns by fertility clinics in the UK and Australia.
Sperm banks in both countries are unable to pay men for their sperm, unlike in the US, where one company, for example, offers up to $900 (£707) for a donation.
And in 2005 British and Australian donors lost the right to donate their sperm anonymously to avoid the child or mother ever finding out who they are.
So men must now be willing to become the biological father of a child for free and accept that the child may contact them when it turns 18.
For what may seem less appealing than being able to donate anonymously and walk away with hundreds of pounds, clinics must come up with new incentives.
And they do this, City University's Dr Laetitia Mimoun said, by using ideas of masculinity to create value for something they can't buy with money.
'This is to say that if you give your sperm you are a real man and you are better than all the other men who cannot do so for whatever reason,' Dr Mimoun said.
Examples of the uber-masculine adverts include one from 2015 which depicts British army officer, Lord Kitchener, in the famous 'Your country needs you' image beside a picture of swimming sperm.
Others show men in superhero costumes with slogans like 'be a hero', and one had a caption purporting to be a fireman saying 'I've saved lives, but never made one'.
Another way of guilting men into donating was what Dr Mimoun called 'classical altruism' – making donating sperm seem like the right, noble thing to do.
A page from the Sperm Donors Australia website showed a smiling man with the headline 'Good men needed for an important job', while another showed a photo of a man giving a piggy-back to a young boy above the caption 'This life changing donation won't cost you a cent'.
Other examples included posters showing athletic men in their underpants or videos showing them cooking barbeques or handing roses to women.
Dr Mimoun said the marketing strategies had worked.
'This has helped the industry in the UK and Australia to resolve their donor shortages to a great extent,' she said.
'It's very interesting that sperm banks are able to procure sperm for free as long as they sell it as a way to affirm the masculinity of donors, especially in today's context when the notion of masculinity is constantly challenged.'
The research was published in the journal Marketing Theory.
Source: The Daily Mail