Police have been criticised for refusing to let a woman who told them she was bleeding leave a cordon for five hours during the G20 protests.
Her GP later told her the bleeding she suffered could have been a miscarriage - though this was never confirmed.
The Independent Police Complaints (IPCC) Commission said the likelihood she miscarried was "low" but called for changes to the policing of protests.
Scotland Yard said there was an "opportunity for lessons to be learnt".
The unnamed 23-year-old graduate recalled events at the protests in April in the City of London.
She told the BBC Two Newsnight programme: "There were hundreds of people behind me and I had nowhere to go so I was being crushed. I couldn't breath, my weight was not on my feet, I was lifted by the full force.
It was a horrendous situation for a human being to be in. I felt completely dehumanised
The female G20 protester
"I was being struck very violently with shields and pushed very violently into nowhere... I was being shouted at and screamed at continuously to get back...
"I remember having a moment thinking 'oh god this is how people die in crowds, getting crushed'".
She also said she was hit on the head, repeatedly kicked in the shins and struck with truncheons which left her arms bruised.
She continued: "I told them I was bleeding - they looked quite shocked in the sense that men aren't very comfortable talking about that...
"They said 'can't you ask someone in there to help?' It made me feel inhuman."
She added she was not offered any medical help and did not request any, but told officers she needed to leave.
"It was a horrendous situation for a human being to be in. I felt completely dehumanised. I was very cold and there was no water," she said.
One man died after the London protests and investigators are looking at other formal complaints about police actions.
Chief Inspector of Constabulary Denis O'Connor has branded the actions of some G20 officers as "unacceptable".
A senior Scotland Yard officer has offered to meet the woman
The woman made a complaint to the IPCC about her treatment by officers at the Climate Camp in Bishopsgate on the day of the demonstration.
She said police kicked and pushed her with shields and batons and that she may have had a miscarriage, a report has said.
As a result, she said, she was left with bruising on her arms and legs as well as heavy intimate bleeding.
The woman had not been aware that she was pregnant and medical staff had been unable to confirm that this had been the case.
The IPCC concluded the woman was forcibly pushed by an officer and she was not allowed to leave the area of Bishopsgate for four to five hours to make herself more comfortable with regard to her bleeding.
It found officers used shields to move the crowd backwards, a tactic which has not been approved nationally by senior officers.
Deborah Glass of the IPCC said, while her alleged injuries were more serious than most suffered that day, her experience "appears to have been typical of many peaceful protestors on 1 April".
She added: "She was caught up in what appears to have been a frightening experience over which she had little or no control.
"Like many others that day, she had no prior warning of the police intention to use force in containing the crowd, and no prior warning of a containment tactic that prevented her leaving when she began to bleed."
It has sent a report to the Inspectorate of Constabulary and Scotland Yard and called for an "immediate change" to the policing of protests.
A spokesman for Scotland Yard said a senior officer had offered to meet the woman to discuss the case.
The spokesman added: "It is only right and proper that public complaints are investigated thoroughly, and where appropriate, independently.
"Though we note that the medical opinion was that there was a low probability of the complainant being pregnant, there is a real opportunity for lessons to be learnt here.
"We are committed to ongoing organisational learning and we are currently examining the HMIC recommendations - reiterated as recommendations in this report - following the Commissioner's request for a review of public order tactics."
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.