Caryn
I do not know how the prednisone can affect the baby. If your sister continues to take prednisone on a regular basis be sure they prescribe something the maintain her bone density. Prednisone can cause severe osteoporosis. My husband has behcets & has been taking Prednisone for many years, he has a fraction of the bone density he should. His ribs can break if he sneazes too hard. You can also buy Citracal +D over the counter. It's calcium with vit.D for better absorbtion. I wish you sister the best during her pregnancy & her struggle with BD.