Just that, I'm 7 weeks pregnant and not sure how much longer I am safe to ride. I have a lovely, steady shire x mare and I have no fear of falling off, I never have since I bought her 5 years ago. I've only been walking since I found out about pregnancy. I do all my riding offroad as I am lucky enough to be on a yard that has extensive hay fields that we can ride round.
It's entirely personal. With DC1 I rode my own horse til nearly 5mths and I would have kept going but I found it really uncomfortable. With DC2 I had moved to a new yard and the hoss was on his toes and spooked massively taking off with me. I was about 4-6weeks diffed and for me, I decided it wasn't worth taking any chances. If I had been at my previous yard I would have kept riding for as long as I was able and then the further into my pregnancy I probably would have only ridden in company.