As I have never been pregnant I am not sure, but I imagine that you can. If you get to the point where it hurts or is stretching or something you can keep it open with a very small ring or fishing line. At least that is what I have heard. But if you go to a place that does piercings I am sure they can sell you something to keep it open, but that will not hurt you.
Don't quote me - never had it done (lol would have to find belly button)
but have been told that if you don't take it out, then it will pop out as the skin becomes so taught.
But then I guess that depends on how big a baby it is and how you are carrying.
I'd leave it a while and if you notice any discomfort then take it out and possibly for the final month just in case baby comes early - last thing you want is an in-ept doctor/nurse/midwife to catch it and rip it out.
I had mine done for 4 years and when I was about 4 months preggy, I took it out. But the hole never closed. I put it back in when I was in the hospital haha! But becuz it wont close, u'l get a ll stretchmark over ur bellybutton ring hole cuz it stretches. But if uve had it that long, it shouldnt close on u in ur pregnancy. Mines back in and im so happy I dont hafta get it repierced again! Lol!