Hey I know it's hard but it is for the best, do not go past 6 months still riding as you can go into premature Labour, preemies can come with all sorts of ongoing health issues, so it is for the best to give it up fir a few months, but like pernicious said just ve around them still, groom and muck out etc, that's all part of the enjoyment of having horses :)
I have 15 horses and it is tough. Best thing to do to keep your mind is just be around them. You can still clean stalls, turnout, groom, and if you know your horse well enough you can still ride as long as you are comfortable and your balance is still ok...just keep to a walk and it's always best to have someone close by.
i was in the same boat .. i barrel raced up untill i was 2 months pregnant and stopped because my OB said it was one of those touchy sports. its been hard but time flys ! id personally just talk too your ob about it and see what they think (: congrats!