The body's iron requirements increase substantially in pregnancy. Iron is necessary for creating haemoglobin, the oxygen carrying protein in red blood cells. Blood volume increases by almost 50 percent during pregnancy, so you require more iron to meet the increased demands. Extra iron is also needed for the placenta and the growing baby. You become anaemic when you no longer have enough iron to create the haemoglobin you require.

Your risk for insufficient iron grows higher if you have severe morning sickness that causes frequent vomiting, if you've had two pregnancies close together, if you are carrying more than one baby, if you have an iron deficient diet, or if you had heavy prenatal menstrual flows.

A normal pregnancy diet requires from 18 to 27 milligrams of iron per day. This amount is difficult to achieve through diet alone, so it is recommended a daily supplement of 30 mg of elemental iron be taken as a preventive measure. Most prenatal supplements contain that amount as a minimum dosage.

The most common cause of anaemia in pregnancy is iron deficiency, but it's not the only cause. Anaemia could also develop from a folic acid or vitamin B12 deficiency, a loss of a large amount of blood or from inherited blood disorders such as sickle cell anaemia. Treatment for anaemia will depend on the cause and iron supplements are not always the solution.
You might not not know you are anaemic especially if your condition is mild. If you do have symptoms you might feel tired, weak and dizzy, which can be normal in pregnancy whether you are anaemic or not. You will have a slight loss of colour, especially in your fingernail beds, the underside of your eyelids and lips. You might experience a rapid heartbeat, heart palpitations, shortness of breath, headache, irritability, and trouble concentrating. Some studies have discovered a connection between severe iron-deficiency anaemia and non-food cravings for substances such as ice, paper or clay, which is a condition known as pica. Don't give in to these cravings. Consult with your healthcare provider as soon as possible.
It's best to take your iron on an empty stomach in order to absorb as much as possible. Take your iron  with water or orange juice, as the vitamin C helps with iron absorption. Don't take your iron with milk, calcium supplements or with an antacid that contains calcium, because calcium interferes with iron absorption. Coffee and tea contain polyphenols that interfere with the absorption of iron as well.
High levels of iron from supplements can lead to constipation. Try drinking prune juice if you suffer from constipation. It can help with regularity and it's a good source of iron. A stool softener may be helpful, too. A normal and harmless side effect of taking iron is that your stools may look darker in colour. Don't consume liver as a way to increase your iron levels. Liver contains unsafe amounts of vitamin A, which can cause birth defects, so it is best avoided during pregnancy.