I'm on 150mg of aspirin per day, which I was VERY reluctant to take. I just turned 40, with a BMI of around 21, so definitely not high BMI, plus I have low blood pressure, not high. The only risk factors for me are my age and the fact it's a first pregnancy, which I didn't think was enough to warrant 150mg.
However, my doctor then scared me with how awful preeclampsia can be: it really can be the point of no return, when the only option is for the baby to come out. And it can be dangerous. So after that, I stopped halving my dose (which I had been doing) and just went ahead and trusted her.
At my last appointment with her, I learnt that the consultant that had advised her to tell me to take 150mg is actually one of London's best. So I am trusting that he really knows what he's doing. Every time I take the dose I worry a little bit, but my doctor is emphatic it's nothing to worry about, when the same can't be said for preeclampsia.
Please report back what you hear, though - as I'm interested to know there seems to be different doses prescribed based on different docs.