Any surgery is traumatic to Lupus patients, or to everyone for that matter. From minor procedures to major surgery! Trauma "Can" cause a flare-up. Some people have had numerous surgeries with no adverse affects. Some are just the opposite.
I would suggest that you try to get as healthy as you can prior to your due date and that you and your obstetrician make a decision that is best for you and for your baby. Of course you have to consider the amount of trauma, but you also have to consider your post-delivery trauma too.
I wish you the best of luck
Peace and Blessings
Look For The Good and Praise It!