Is it safe to take prednisone while pregnant or breastfeeding?

Yes. If you have a condition that your doctor thinks Prednisone is necessary to treat, it is safe during pregnancy.
Yes to some extent. It can worsen some problems that occur with pregnancy, including gestational diabetes, and also hypertension. Because it induces Insulin resistance, large babies are more common. Afterwards, it is not a problem with breast feeding!