First, I would encourage you to go ahead with both decisions. You know it. There is no perfect time to have a baby.
Second, Some universities hire you as a research assistant and you have a double status as an employee and a student. Do you have already an offer? If so, you can ask directly. There is no shame about it. The other case is that you are a student and get a stipend. Usually stipends are less money.
I think you will not be the first person to do this. One year gap is reasonable and should not affect your return. It is very unlikely that this causes administrative problems but some supervisors may not like it but it is your decision at the end.