I have always been told not to ride while pregnant. Your best bet is to call your doctor and talk with them
You probably shouldn't be riding horses if you're pregnant..
My doctor approved of riding. I have been an avid rider since I was a kid. Just wasn't sure how hard of a jolt would be considered dangerous.
I had a car accident at 13 weeks. Car smashed into the side of my car at full speed and my car spun around. Huge jolt and was very shaken up. I called my midwife and she said if there was no impact to my belly I should be okay. I had to monitor and changes in discharge, bleeding, feeling in my tummy etc. The only thing that may have occurred with a big jolt in that your placenta could detach which is bad so watch for bleeding/changes.
I was advised not to be jumping into my pool during summer when I was around 18-26 weeks. There is also a big wharf where I live and love jumping into the ocean and again was told to stay away in case of a jolt big enough to detach my placenta. Hope that gives you a little insight :)