Well, I cannot give you specific advice on the PE exam since I haven’t taken it. But I have done the working with a baby/new mom thing. I agree with you to not plan on doing anything during the first few months. Hopefully you’ll have an easy baby and quick recovery but many things could prevent you from wanting to jump back into work at 3 months: colic, sleep problems, food allergies, PPD, etc. You won’t know how much you can do until you meet your baby and find out your new dynamics as a mother. I would suggest getting the study materials but don’t sign up for a test just yet. That way you can decide on a good pace without the pressure of a deadline. If you are able to get your baby on a good routine then it will be easier to set aside time each day for studying while they sleep. But remember, you also have to catch up on laundry, cook, clean, and take a nap during those precious hours too! If you have family close by maybe you could arrange to have them watch your baby for a few hours each week for your studying. Or if you have a spouse/significant other you could say “every Thursday from 7-9pm is PE review time” (for example).
Another thought I have for you is… if you’re seriously deciding on taking some time off work and becoming a stay-at-home-mom for awhile (which I am currently doing and I LOVE!) you might want to consider putting off the PE exam until you’re ready to go back to work. That way it will help you review basic principles you’ve forgotten over that time and it also shows a future employer that you’re still a competent engineer who hasn’t forgotten everything while being a full-time mom.
Best of luck to you and your new adventure as a mommy! And remember, they are only little for a short time so enjoy your baby and don’t put pressure on yourself to get everything done ASAP. There will always be time for the PE, but only a brief time to snuggle with your baby. I think as engineers we’re wired to be as efficient as possible and it is hard to just allow ourselves to sit and enjoy the moment. That was a hard transition for me to make and I regret not allowing myself to quit my job sooner to be with my baby. But I cherish the sweet moments we have now and hope to have many more with my two girls who are due in May. Many women can make the working mom thing work, but for my family being a stay-at-home-mom was the best option for us. :-)