Women using unregulated websites to find a sperm donor have been harassed and sent photos of miscarriages, the BBC has found.
There are strict criteria for NHS artificial insemination and many women say private treatment is too expensive, so they turn to the internet.
One woman told how a potential donor she met turned out to be married and had had a vasectomy.
A fertility expert called for unregulated sites to be shut down.
Online sperm donation is not illegal but it must be provided free, although expenses can be covered.
Some online donors offer artificial insemination (AI) and others natural insemination (NI) – effectively unprotected sex with a stranger.
‘A few idiots’
“Sarah”, 26, from Yorkshire, is single and said she wanted a baby without a partner.
She told BBC Inside Out the cost of private treatment was too high and going online meant the treatment was free, although she did experience problems.
She said: “There have been a few idiots that you really wouldn’t want to interact with, because they do harass you or start sending you images you really don’t need to see.”
‘Messages of miscarriages’
Couple Kirsti and Danielle, from West Yorkshire, said they had faced pressure from men online to use NI.
Kirsti said: “Some people try to put you off by sending you messages of miscarriages and stuff, like if you do it that way, this will happen.
“So they are trying to change your mind for the method, so then you have sex with them.”
Sarah did meet one man online but he was not as he seemed.
“Ultimately it turned out he was married and that he’d actually had a vasectomy, so was in no way viable at all,” she said.
“It made me feel like I couldn’t trust people on the site.
“I think they do need to be policed by a proper organisation, not just some random person out there because you don’t know if they’re safe because there’s no proof of who you are on there.”
Registered clinics carry out a strict screening process for sexually transmitted infections and infectious diseases and check potential donors’ complete medical history.
Alison Lamont, from one of these, Newcastle Fertility Centre, said it was difficult for the clinic to find donors.
Fertility expert Dr Larisa Corda said the growing trend of online sperm donation was “really alarming”.
She said: “I think women are putting themselves in an incredibly vulnerable position medically speaking and secondly the potential for abuse.”
She said she believed the cost was a real barrier to a lot of women and it meant they were putting themselves in vulnerable situations, such as using unregulated online donors.
“In the ideal world, I’d love to see them shut down because I think women’s safety and welfare has to be paramount here,” she said.
Dr Tamara Turner-Moore, senior lecturer in psychology at Leeds Beckett University, is involved in a study about online sperm donation, which she believes will be the first of its kind.
It will look at the number of websites offering sperm, what the sites look like and the profiles of men using them and how they present themselves.
The study will also look at women’s experiences including those who have experienced sexual violence by online sperm donors.
It hopes to get an idea of the number of such sites and the problems women face and raise awareness of them.
You can watch the full story on Inside Out, North East & Cumbria, on Monday 24 September at 19:30 GMT on BBC One.