Me, sort of! I'm a research masters student who should be going on to PhD next year. Like you, we planned the pregnancy as I'm 32 and so would be 36 if I waited to finish a PhD (and I work too, so no certainty that I'd manage in 3 years). Really glad to see this thread, as I thought I must be completely mad, but if I am, I'm in good company! The plan is to do as much groundwork before May as possible and then write up the following year and go into the next year's funding cycle.
I had to tell the university very early, as unfortunately I've been really unwell (I'm only 11 weeks now, and they've known for 3 or 4 weeks as I'm NEVER EVER off and they were worried), and I have to say they have been fab. I can understand your reservations though: as a funded student myself, I was worried about what they might say. My scholarship is from the university and so I don't have to worry about stopping and starting, but it might be worth you making preliminary enquiries (if you haven't already) if you are research council funded, as they might have specific policies. I think the great thing about a research degree is that it is just that: you are ultimately in charge and so it isn't such a big deal to pick it up and put it down as long as you are organised, which you obviously are! I've got a couple of taught bits in my MRes, and they are a pain at the moment, as I'm missing classes while I cuddle the loo/try to stay upright etc. I've decided to do much the same as you: bump will hatch in May, I'll probably stop until Christmas, but go back sooner if I can. I'll have 9 months off my part-time teaching job though so that I can phase the return more manageably.
If you don't mind me asking, how old was your first child when you went back to university? My SIL is doing an undergrad degree, but her boy is 4 and so free nursery care has kicked in for them. I'm a bit worried about how I'll juggle it all, especially if we have another before I'm done!
Thanks again for starting this thread!