Meal replacement drink and Vitamin supplement?

Hi everyone!

Question for all your nutrition gurus out there.

I'm pregnant (YAY! - its a boy!). As part of a healthy pregnant woman diet plan, I should take a daily vitamin supplement.

Currently, I take Centrum Prenatals. I'm sure they have everything I need in there, except, they make my tummy sick, sometimes even if I take it with a full meal.

I recently tried a meal replacement drink called Similac MOM (meal replacement for preggo ladies like me!).

My question is...
Should I take the meal replacement+ the prenatal vitamin?
Can I just take the meal replacement?
I really want to discontinue taking those Centrum Prenatals since they make my tummy sick.

Also, I don't think it is good if I take too many vitamins, as an excess intake of Vitamin A has been linked with some birth defects.
Opinions???
Thanks!