I had my first baby in the middle of 3rd year out of 4 for EM. My residency had me scheduled till 41 weeks(!). I prayed for an early delivery but it didn't happen and I worked till just shy of 40 weeks, was about to start a string of 3 overnights on 40 and 0, but then my chief said I could make up the rest of the shifts. I indeed made up all the shifts covered for me by my co-residents, some before and some after the baby, so I didn't feel bad about that aspect. We also didn't send anyone from our residency to our community hospital for one month and I made up that month after official end of residency (July and part of August - they let me do it part-time .
I had baby 2 1.5 years into attending, and baby 3 3 years after that. I was more stressed having babies while attending because there wasn't the extra help/coverage around day to day after return to e.g. take 1 pumping break for 15 min during the entire 10 hours etc. I also felt like it was easier to transition back in during residency because I had my attending there as well. (Was afraid of getting rusty.)
I also took longer to get pregnant on my 2nd/3rd (was 34 for my first), and had a miscarriage between them.
This is rambling a bit, but I think it might have been better to start younger and have 2 during residency if possible.