Prenatal vitamins are almost universally given to pregnant women today. But having too much or too little of certain vitamins and minerals in pregnancy can cause problems. For example, large amounts of vitamin A have been found to increase the prevalence of craniofacial (head and face) defects. On the other hand, maternal deficiency of folic acid, a B vitamin, or zinc, a mineral, has been associated with birth defects. It is important to always to follow your doctor’s advice on the recommended doses for vitamins and minerals.