Should I take iron supplements in pregnancy?

5 things to know:

1. You will be tested for anaemia at the beginning of pregnancy, then again at 28 weeks. 

2. The baby uses up iron stores and also the blood dilutes slightly so some women can become anaemic in pregnancy.

3. If you are not anaemic and have normal iron stores, then there is no need to take extra iron in pregnancy.

4. Iron is found in many foods including meat, fish, pulses, nuts and green leafy vegetables. 

5. It is important to avoid anaemia to avoid complications around the time of birth, especially the risk of heavy bleeding after the baby is born.

What is iron and why is it important?

Iron is a nutrient that we need to make haemoglobin. This is the molecule that carries oxygen in the blood, so it is vital for the growth of the baby, and general health in pregnancy. If haemoglobin is low, most likely because iron levels are low, then this is anaemia and it can cause tiredness, and sometimes even fainting in pregnancy. It is important to maintain a normal haemoglobin in pregnancy, as when the baby is born you will bleed and lose blood to some degree. Some women have a heavy bleed, and this is known as a post partum (after birth) haemorrhage.

Is low haemoglobin normal and what can cause it?

We know that women who have a low haemoglobin are more likely to bleed more after the baby is born. During pregnancy, it is normal for the haemoglobin level to fall slightly. This can be because the baby is using more of your iron stores and your diet cannot keep up. Therefore, you can become anaemic later in the pregnancy. It is also usual for the haemoglobin level to fall during pregnancy slightly due to dilution of the blood after around 28-32 weeks. This is because the composition of the blood changes slightly with normal pregnancy to contain more fluid and fewer cells. This is normal and does not need to be treated. However, this can sometimes push the haemoglobin in a blood test down into anaemic levels.

Some women also go into pregnancy with a low haemoglobin level if it has not been long since their previous pregnancy, they are still breastfeeding or they suffer heavy periods.

The most common cause of a low haemoglobin is low iron in the diet. Iron is found in lots of foods but can sometimes be difficult to absorb. The best sources of iron are meat (all forms), pulses and green leafy vegetables. Some foods contain added iron including some breakfast cereals. It is also important to recognise that anaemia is not always due to low iron as it can also occur if you have other dietary deficiencies such as folate or B12. 

Do I need to take iron supplements?

If you have normal haemoglobin and iron stores in pregnancy, then this means that you are eating enough iron in your normal diet and, most likely, there is no need for you to take any extra iron. Some pregnancy multivitamins contain a small amount of iron. This will not do any harm but will not be enough to treat anaemia. The midwife will measure your haemoglobin (in a full blood count) and will probably also measure iron stores using a test for ferritin at the beginning of the pregnancy. Haemoglobin will also be measured again at around 28 weeks. The normal ranges for these tests are different during pregnancy compared to non-pregnant women. If these tests are low, then the midwife will suggest that you take iron tablets during pregnancy.

How do I take iron?

Iron is usually taken as a tablet, but it can also be taken as a liquid. If possible, take this on an empty stomach and with a drink that contains vitamin C. This will increase the absorption. Sometimes, iron supplements can cause an upset tummy. This can mean diarrhoea or constipation. It is common for iron to make your stools turn black – this is nothing to worry about. If the side effects mean that you cannot tolerate the iron tablets, the first thing to do is take the tablets with a mean instead. Sometimes a lower dose or a different preparation or even the liquid can help.