Flintstones vitamins are fine to take by like clysta said you'll also need to take an iron suppliment because they don't have enough iron in them.
I used the Flintstones Complete chewables for a little bit while pregnant when I couldn't take my normal prenatals. 18 mg of Iron isn't too much, it's not enough. When pregnant you need around 28 mg of Iron. They should all have folic acid in them, mine did as well. Mine had 400 mg in them.