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 :)
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.
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.
You probably shouldn't be riding horses if you're pregnant..
I have always been told not to ride while pregnant. Your best bet is to call your doctor and talk with them