A few points.
1) Until the end of the month when the new Road Traffic Act comes in to force (Traffic Management Act 2004) serving Penalty Charge Notices via CCTV is unlawful EXCEPT where there is a notice saying so, i.e Red Route, Controlled Bus lan etc.
2) A fine will stay live, in theory for ever. Do not be fooled by people saying they have hundreds. I am sorry to say their day will come. Whether bayliffs, clamping and removal or in the worse case scenario, a court case.
3) There is no special provision for pregnant ladies
4) If you do wish to contest the fine, my advice will be pay it first. Why?
a) If it goes to court they can not ask you to pay a higher rate
b) You will get you money back if successful.
c) It shows lawful duty to pay penalties. Paying a fine IS NOT an admission of guilt.
5) Should you be driving if your bladder is that weak?
6) By what you have said, I am afraid you deserve the fine. Harsh but that is the law.
7) Depending where you live, not all parking is as yet de-criminalised
8) You CAN NOT pee in a policemans helmet. Old myth.
9) Good luck.