Hi OP, just to add my two cents:
I am a p/t MA student at one of the major unis, pregnant with DC2, fell pregnant with DC1 whilst doing my studies and this is what happened to me and how I coped:
On a one-to-one basis, everyone was very kind and supportive, as well as a little (academically) curious. I was allowed to put my studies on hold when morning sickness and a full time job got too much and I fell behind. Intending to return to my studies when DC1 was 5 months, I didn't due to PND, but again I was granted another suspension of studies (these suspensions meant I wasn't able to access the library for almost two years, which was a pain). On returning in January this year, just after getting my BFP for DC2, I am determined to complete before new arrival in September. Uni have again been as supportive as they can be.
However
Things to check out are not just how your uni/college/dept will be with you whilst you are pregnant, but also how they will be when you choose to return. For example, I had an uphill battle trying to find anywhere I was able to use to express breastmilk. In the end, I was given the choice of two toilet rooms, or a room full of human remains in sealed boxes. This latter option also came with the added luxury of a chair. Woop.
This link is to a document focussing on the issues surrounding pregnancy and studies, and I hope it proves helpful to you. I would really advise being as open and upfront about your requirements and hopes for your PhD as you can as soon as possible. There is nothing to stop you from doing both. As one student in my lab said to me the other week, we expectant students are an example to other women that you can be both a mother and an academic. It is so important that other students see what you are doing, and that your institution is made aware of all of your requirements and wishes.
Good luck!