you can ride only with the expressed permission by your ob-gyn. since i do not know you the stage of your pregnancy or your medical/obstetric history it would not be prudent to offer you a patient-specific response in this matter i'm no expert on this but i'd say the activity your questioning is unsafe due to the height off the ground may be dangerous if you were to fall and an accident with an animal that size might be fatal with or without pregnancy. considering the fact that when i was pregnant i was restricted from participating in any extracurricular activities i'm assuming because they were hazardous. my suggestion is to stay safe and make careful decisions for you and your baby.
is it okay to ride horses while pregnant? . i have ridden for years and it's not like i would ride crazy horses or go faster than a walk. i know what im doing and don't see the harm in a slow walk.