Is it safe in pregnancy?

I drink 1 cup of slim fast every day, but not as a meal replacement, just for the vitamins and minerals. I don't like milk plain so that's the only time I drink milk too, but I take calcium supplements. Now that I just got my BFP, is it safe to keep doing this? I've started taking a prenatal vitamin but it only has 80% of the recommended daily intake of calcium for pregnant women.