1. You are going to have to address your pregnancy, lol
... I'm sure you are "visible" enough that the question is going to come up. Most likely if they feel you are what they want, they may make your hire date after you have the baby and after your 6 week check up, so about June-July, about the next time there is a new grad cycle, OR they may start in April, go through the hospital orientation, then wait for your nursing orientation after you have the baby and 6-weeks check up.
2. Usually the 30 minute interviews are like the screening process...you are a new grad, so most likely, they may have a few units they may want to place you. If you have a prior work history, you will get into your experience, how your experiences shaped you and your nursing practice, as well as your experiences on your clinicals may come up. Based on this first process, they will select a unit for you to interview, if all goes well.
Congrats on your baby and good luck on your interview!