Most rheumatologists keep their SLE patients on Plaquenil while pregnant. Experience over time has shown it to be a very safe drug to take, with the benefits outweighing the possible risks.
My rheumy wanted me to stay on 400mg a day, but I did reduce to 200mg a day after I knew I was pregnant. That was my choice, and actually against his advice, but I knew for me 400 was actually a bit too high for my weight/size anyways. I did quite well during pregnancy - it brought me into remission despite the lowered dose and was even well for a few months after pregnancy.
Good luck to you if you're wanting to get pregnant soon and congrats if you're already there.
