Requirements for Iron varies widely amongst gender. Adult men require about 8 mg per day while pregnant women need up to 27 mg per day. Reproductive age women need about 18 mg/day due to iron losses during menstruation.
Even though the body has mechanisms to facilitate high conservation of iron, pregnant women will need to absorb about 3 times as much iron as before conception. Low iron stores in the body can be simply revealed from a blood test that measures ferritin. Best to make sure body Iron levels are replete at the start of pregnancy.
Iron from vegetarian sources is generally less well absorbed through the gut and as such vegan and other nonmeat eaters need about twice as much iron containing food as the carnivores.