Quote From Trilla:
PNV, unless you are at the end of your biological clock I'd advise against the PhD and baby. I did mine with teen kids and a job, did it in 3 years on the dot but, boy, it was the hardest thing I have done. I have aged 10 years in these 3...And that's 3 years of my kids' life I'll never get back. i think that doing the two you won't enjoy neither the phd or parenthood.
I agree with this. Three of my friends have had a baby whilst doing a lab-based PhD and all of them wished in some way or another they didn't. For some it was planned without fully appreciating the consequences, for others it was unplanned. If there's no rush to start a family, then just wait it out. It's only three years. A PhD is a big enough commitment without a baby as well.
Having said that, none of my friends had their mother in laws around, in fact in two out of the three cases, the mother went back to work one month after giving birth and the father was the care giver (he wasn't doing a PhD or working). In the other case, the mother wasn't doing a PhD and the father was 6 months from finishing the thesis.