Is it safe to have or get a belly ring while I'm pregnant?

DO NOT GET. UNNECESSARY PROCEDURES DONE WHEN YOU ARE PREGNANT. A piercing is always ELECTIVE!!.
Generally yes. The physical act of piercing is not something that should affect pregnancy outcome. However, because there can be complications and your belly button will undergo some changes during pregnancy i would recommend avoiding any unnecessary procedures. Wait until after.
Yes and no. The belly button ring itself is pretty safe. However, as your belly stretches the skin over the ring will get thinner and the ring may pull through. Most women take their ring out before they hit the third trimester.