Prenatal vitamins are specifically formulated to provide essential nutrients for pregnant women and their developing fetuses. These vitamins contain various nutrients, including folic acid, iron, calcium, and vitamin D. While weight gain is common during pregnancy, no direct evidence suggests that taking prenatal vitamins causes weight gain. Some studies have shown that prenatal vitamins may help prevent excessive weight gain during pregnancy. However, as with any supplement or medication, it is important to talk to your healthcare provider before starting to take prenatal vitamins or if you experience any unexpected side effects.