They just make sure your body has enough vitamins and minerals for both you and the baby. Don't stress too much about them, just take them after your meals.
They work by supplementing vital nutrients like folic acid for neural tubes, and calcium for bone health. Always take them with water and never skip your prescribed doses.
Folic acid and iron pills support baby's overall development. But along with these, make sure your thyroid or other specific pills are monitored by your doctor monthly.