Prenatal supplements are generally considered safe and well-tolerated when taken at the recommended dosage. However, it’s important not to exceed the recommended daily intake during pregnancy, as higher doses of certain vitamins and minerals may be harmful to the fetus (e.g., iron, folic acid, zinc). Studies specifically addressing the risks of exceeding the upper limit (UL) of these micronutrients during pregnancy are lacking, except for vitamin A. Excessive intake of vitamin A (above 3000 μg)[1] during pregnancy is known to have teratogenic (i.e., birth-defect-causing) effects.[2][3] In some prenatal supplements, vitamin A is substituted with beta-carotene, which is converted into vitamin A naturally by the body as required and does not appear to be teratogenic at high doses.[4]
Another potential side effect of taking prenatal vitamins and minerals is constipation, primarily caused by iron.[5]