Folic acid is recommended before conception and through early pregnancy to lower the risk of neural tube defects such as spina bifida, and vitamin D is commonly advised throughout pregnancy and breastfeeding. Some women, for example those with a higher risk of neural tube defects, certain conditions, or a history of deficiency, need different amounts, so this should be individualised.
A dedicated prenatal multivitamin can be convenient, but it is important to use a pregnancy-specific product because some nutrients are harmful in excess during pregnancy. In particular, high-dose vitamin A (retinol) and liver, which is very high in vitamin A, are best avoided as they can harm the developing baby.
Iron may be added if you become anaemic, and iodine and omega-3 are sometimes discussed. Because needs vary and some supplements are unsafe, confirm exactly what to take, and what to avoid, with your doctor, midwife or pharmacist rather than self-selecting products.