Welcome to the forum and huge apologies for taking an eternity to reply to you.
There is quite a big window of opportunity with aspirin. Depending on how severe your experience of PE as previously, some consultants suggest prior to conception, but all would agree commencing before the 12th week of pregnancy as this is when the placenta forms and where the cause of PE starts.
Aspirin is stopped at about 35/36 weeks to allow your blood to 'normalise' prior to delivery although the effects can be easily reversed if the benefit of continuing outweighs the risk.
I hope this helps and look forward to hearing happy news in the future. If there is anything else I can help with please do let me know.
Every Woman is entitled to understand what happened in her pregnancy when pre eclampsia strikes. I hope to be able to support that process.