Natural insemination is thought to be three times more effective than artificial insemination.
Men are offering their sperm to women through natural insemination or partial insemination.
Women desperate to become mothers are increasingly signing up for sperm donation websites where men are offering 'natural insemination' only.
Sites including co-parents.net, co-parentmatch.com, spermdonorforum.com, donordaddy.co.uk and pollentree.com advertise themselves as 'dating websites', forums aiming to link people wishing to conceive or 'co-parent' a child.
But while such donations are traditionally carried out artificially, a rising number of women are opting to do so naturally, by having sex with their donors, because it is believed to be more three times more effective than artificial insemination.
Many men on these sites will not offer artificial insemination (AI), only natural (NI) or partial (PI), leading some critics to believe they are simply targeting vulnerable women for free sex.
On one forum, Tadpole Town, a potential donor writes: 'I'm a donor, and I only help by NI or PI. Have had quite a few ladies try the guilt trip to try to get me to AI, not for me though.'
So while regulated HFEA clinics - which charge £2,000 per cycle - screen all donors for STDs and hereditary conditions, 'free' sperm donation websites do not. Similarly, clinics protect the identity of donors until any child produced is 18, while the conditions of donation via free websites is entirely up to the co-parents.
Zita West of Zita West Clinics, an HFEA-regulated site, told Croydon: 'When a woman's desperate for a baby and can't afford a clinic, she's vulnerable.
'She may be panicking about her biological clock ticking and might then risk meeting one of these men.
'But she won’t know anything about his genetic background or if he’s been screened for HIV. These sites should be regulated.'
Source: By Martha De Lacey Daily Mail, 1 May 2013.