Not exactly the same situation, but I've recently found out that I'm pregnant and I'm in my final year of my PhD.
What I did was switch to part-time immediately (at my uni you can't switch from full to part-time during the writing up year). I'm going to get as much work done as I can before the baby arrives, take a year out officially but ease myself back into the PhD after about 9 months.
Is switching to part-time an option for you? Most funding bodies are fine about this if you have funding.

Also you've got to consider things like childcare for when you return. Could you afford a childminder or do you have family close by?
You could postpone for a year, but then there's always the fear that you might find it harder to get back into research and study if you haven't done any for a while. I also found the first year of the PhD by far the hardest as you have the bulk of the research to do and you're trying to scope and define your project which takes a lot of brain power and reflection! In all honesty, probably wouldn't have returned to it if I'd had a baby at any point during that period, obviously everyone is different, but if you can get a good foundation in before you have your baby then it would be making things easier to come back to.

Obviously everyone's experience is different and I hope some of the other parent posters give you their advice too.

Good luck with what you decide!

Hi all,
This thread might be very useful for me as I'm currently pregnant and due my first baby in April next year.
I was in my third full-time year of my PhD due to end in February but when I found out I switched to part-time so I can come back part-time after ML. I'm still working full time though to make sure I get as much done as possible before the baby arrives. Thankfully I'm arts/humanities based so don't have any lab work etc to do and I'm at the drafting of chapters stage now.
No doubt I'll be on here desperate for advice and support over the coming months!