I have a maternity one in now. Very comfy as its a type of plastic that bends with movement.
Your naval is your belly button. Lol and I just recently took mine out, im 39+2. I took it out bc it ripped when I was putting a tank top on. Not all the way through but it definitely hurt so you can keep it in as long as it's comfortable but just be careful.
U may get a bad stretch mark from it I did! Only one on front of stomch is my belly button ring ha
What's a naval ring if you don't mind me asking
7 months and still have mine in. Getting a pregnancy one soon though
My best friend kept hers in through out her whole pregnancy, it really depends on how well your skin stretches and your own preferences.
Go to spencers they sell a plastic thingy for when you get prego :)