Congratulations on your baby - I've posted before about riding when pregnant and I would urge anyone who is pregnant to think very carefully about it.
I rode up to the 7 month mark during my first pregnancy as I judged that the risks to my unborn child were minimal. I had my own horses and I had no problems until the last ride I'd planned to do before hanging up my saddle and turning my mare out for the summer. My mare shied at something and since my balance was not quite as it should have been due to the bump (which was pretty small) I wrenched my right hip badly. It took me a while to be able to lift my leg to be able to get off the horse when we got back from the hack.
I recovered from that although I did have problems walking up stairs for sometime.
Roll on 4 years, I fell pregnant again. From 4 weeks in I suffered badly from pain in my right hip, I developed pretty severe PGP and I am still having problems with the SI joint and a generally twisted pelvis. This is over 7 years later.
So my advice, think really carefully and remember that your ligaments are getting looser and looser. I weighed up the risks and thought that if I was sensible the risks to my unborn child were minimal but I did not appreciate how pregnancy hormones can relax your ligaments etc and so you can damage yourself as a result of something that would have otherwise been innocuous.
Sorry for the ranty ramble. I feel quite passionate about this one and I wish someone had told me when I was up the duff the first time as I don't think I'd be in the mess I am in now. Mind you, I probably wouldn't have listened as I was riding 6 times a week before I got pregnant and no-one was going to come between me and my mares!.
Wishing you all the best for you and your baby.