Victoria Poskitt, 40, who was five months pregnant at the time of the incident, resorted to sitting on the floor when she started to feel ill on the Surbiton to Waterloo service.
She claims none of her fellow passengers gave up their seats to her, and South West Trains refused to grant her a 'pregnancy pass' - as these are only available to women who are more than 20 weeks pregnant and in possession of a season ticket.
'I thought [South West Trains] might be willing to make an exception, particularly after I told them about what happened, but after conversations with various managers they've flatly said "no", saying policy is policy.'
Mrs Poskitt is campaigning to be given the upgrade which she believes will make all the difference to the last few months of her pregnancy.
'I don't honestly know [what to do next]. I keep trying with South West Trains, I'm throwing myself at their mercy.'
The pregnancy passes available with the network allow pregnant women to sit in first class, and in the last year South West Trains have handed out 575 of these upgrade tickets.
Mrs Poskitt was unfortunately ineligible for the upgrade because she was not within 20 weeks of her due date and she did not hold a season ticket.
A spokesman for South West Trains Network Rail Alliance said: 'We are sorry to hear that Ms Poskitt felt unwell recently on one of our services.'
'We have the most extensive upgrade scheme of any rail operator to help our customers who are expecting a baby.'
'As on other forms of transport, our experience is that fellow passengers will give up their seat for mums-to-be and other customers such as elderly people and we are sorry and surpassed this did not happen.'