iron supplements and pregnancy

Last reviewed 09/2023

Iron supplementation should not be offered routinely to all pregnant women (1)

• it does not benefit the mother's or fetus's health and may have unpleasant maternal side effects

Iron is depleted in pregnancy due to the increased requirements of foetus and placenta, and the rise in red cell mass. The patient may present with a picture of chronic tiredness and a haemoglobin concentration of 10 g/dl or lower.

However, trials have shown that the suspected benefit of iron supplementation is not fulfilled. The hazards are:

• at high haemoglobin concentrations, the risk of perinatal mortality and low birthweight is increased
• many women develop side effects from taking iron e.g. heartburn and nausea
• consistently trials have shown iron to have no beneficial effect on mother or fetus
• iron tablets are regularly taken in accidental overdose by children
• iron may interfere with the absorption of other minerals

Hence, iron supplementation is only advisable in the following groups:

• women at high risk of anaemia due to poor nutrition or heavy menstruation after screening in the first trimester
• later in pregnancy, those with Hb < 10g/dl and MCV < 84fl

Dietary changes are a preferred first-line measure, and indeed, in those on an adequate diet, the gastrointestinal tract physiologically increases its absorption of iron in response to the increased demands.

Reference:

• (1) NICE (2008). Antenatal care.
• (2) Drug and Therapeutics Bulletin. Routine iron supplements in pregnancy are unnecessary 1994;32 (4):31-32.
• (3) Barrett JFR. Absorption of non-haem iron from food during normal pregnancy. BMJ 1994; 309: 79-82.
• (4) Doctor (August 23rd 2005): 22-23.