Is it safe to ride horses while pregnant?

No: Any potentially dangerous activity should be avoided during pregnancy. Also low impact exercises are encouraged.

Ask your OB: As your OB knows you and your condition and if you do it needs to be slow as the bouncing could cause a potential problem and i assume u are a good rider because a fall would be potentially disasterous, sometimes you need to sacrifise a few things during pregnancy because the potential risk and consequences is not worth the pleasure and u have the rest of your life to ride after pregnancy.