Hi Blossy,
Im only a newbie to riding and have finished all my childbearing for this lifetime (3 young boys is enough to put me off having any more children!!!!! I DO NOT have the energy to keep up with them, let along lug around another baby belly at the same time
) and I would say, be safe and ride within your limits as the other ladies have suggested.
BUT I do remember my osetopath saying that you have to be careful with bike riding while pregnant as sitting on the seat position can (not WILL) put pressure on your bones by sitting on such a small seat and can lead to problems from pelvic instability. So if you start to feel uncomfortable in the back of your legs, bum and lower back it could be the pressure from bike riding that is creating the discomfort. So just something to keep an eye out for. (mind you, getting uncomfortable in those areas is part of being pregnant too, but I know that bike riding can increase that discomfort through those areas.) I had pelvic instability throughout my 3 pregnancies which I thought was sciatica and it is quite difficult to deal with while being pregnant so hopefully you won't have to worry about it at all - and life will be all good!!!!
Congrats on the news too!!! Very exciting for you both!!!