I forget the measurements on the baking soda or oatmeal to water ratio so Google that if you'd like to try
I never had hives while pregnant but I know some home remedies. You know the shampoo selson blue? It makes your rash feel soo much better if you use it as body wash. Try calamine lotion as well. You can try taking a bath with baking soda or collodial oatmeal. Although I know its hard not to don't scratch!! It'll make em worse