Iron in Pregnancy

Published in the Winter 2008 edition of Nurture - a magazine devoted to parenting naturally.

Pregnancy is a normal, physiological state and nature is really good at adaptation, so I have never come to terms with the concept of routine iron supplementation during pregnancy. Iron supplements are often not tolerated well and cause side effects like nausea and constipation, which are associated with pregnancy even without iron. In Australia, we have the enormous privilege of readily available, fresh food and great nutrition, especially compared to many other countries. This discussion is about well, healthy women, who have good nutrition and not women who are anaemic or undernourished.

A mother’s blood volume during pregnancy increases dramatically by between 30 and 50 per cent to meet the extra demands of the placenta and baby. The rise begins at about 6 weeks and continues until about 32 to 34 weeks of pregnancy, when it stabilises. Blood is made up of fluid (called plasma) and cells. There is a 50 per cent increase in plasma volume and approximately 18 per cent increase in red blood cell mass. Because the increase of fluid volume to cell mass is disproportionate, certain values in a blood test are affected. One in particular is the haemoglobin concentration which decreases, resulting in what is sometimes called ‘physiological anaemia of pregnancy’. However, an appropriate plasma volume expansion and its associated decrease in haemoglobin has been recognized as a sign of 'pregnancy well-being' and should not be considered to be a medical condition that requires treatment (Little, Brocard, Elliot and Steer, 2005; Scholl, 2005; Ross and Idah, 2004).

The World Health Organisation classifies anaemia as a haemoglobin level of 11g/dL or less but recent studies have found that there is an optimal range of haemoglobin concentration for pregnant women of between 9g/dL and 11g/dL, at which birth weight is highest and perinatal mortality is lowest (Little, Brocard, Elliot and Steer, 2005). “There is a need, therefore, to differentiate between physiological adaptation and a pathological condition” (Bewley, 2004, p. 794). It may be that the definition of anaemia needs to be reviewed with consideration of the normal physiological adaptation of pregnancy, so that normal, healthy women are not labelled with a “pathology”.

In the past, pregnant women were routinely prescribed iron supplements. Recent studies have shown that, not only is this unnecessary, but that it may be deleterious to some women. A 2005 study published in the American Journal of Clinical Nutrition shows a link between maternal complications, such as gestational diabetes and increased oxidative stress during pregnancy and taking iron supplements and increased iron stores. The author states: ‘while iron supplementation may improve pregnancy outcome when the mother is iron deficient it is also possible that prophylactic supplementation may increase risk when the mother does not have iron deficiency or iron deficiency anaemia (IDA). Anemia and IDA are not synonymous, even among low-income minority women in their reproductive years’ (Scholl, 2005).

Another study has shown an increase in premature birth in women who had supplementary iron when their iron stores were good (Lao, Tam and Chan, 2000). Little, Brocard, Elliott and Steer (2005) suggest that supplementation with iron should be considered for pregnant women with a haemoglobin level of less than 9g/dL.

Anaemia can cause a pregnant woman to become excessively fatigued, have impaired immune and digestive function and, in severe cases, can increase the risk of perinatal problems (Bewley, 2004).

At 36 weeks pregnant, a woman absorbs 9.1 times more iron from her food than at 12 weeks of pregnancy (Barrett, Whittaker, Williams and Lind, 1994) - further evidence of how well the human body adapts to the normal process of pregnancy.

Good dietary sources of iron include lean meat, especially lean red meat and liver, beans, nuts and seeds, dried apricots and dates and green leafy vegetables. The iron found in meat is known as heme iron and is much more bioavailable than non-heme iron. Other factors that positively influence how much iron is available or absorbed include: combining it with vitamin C; eating heme and non-heme iron; and cooking non-heme food in an iron pot like a cast iron skillet. Factors that inhibit iron absorption include the tannins in tea, large amounts of caffeine, high fiber foods and a high intake of calcium.

If supplements are necessary there are varying preparations that contain different kinds of iron at different levels and some contain vitamin C. Generally, the higher iron content tends to cause the most difficulties. If iron levels are only slightly low or a pregnant woman is vegetarian and concerned about her level of dietary iron, then a low dose iron supplement may be the best alternative. In order to increase absorption, the supplement should be taken with vitamin C and away from tea, coffee and high fibre foods. It’s probably best to have individual advice that is specific to the circumstances, if supplementation is recommended.


Barrett, J.F., Whittaker, P.G., Williams, J.G. and Lind, T. (1994). Absorption of non-haem iron from food during normal pregnancy. British Medical Journal, 309(6947), 79-82.

Bewley, C. (2004). Medical Disorders of Pregnancy. In C. Henderson and S. Macdonald (Eds.), Mayes Midwifery: A textbook for midwives (pp. 793-795). Edinburgh, Bailliere Tindall.

Lao, T.T., Tam, K.F. and Chan, L.Y. (2000). Third trimester iron status and pregnancy outcome in non-anaemic women: pregnancy unfavourably affected by maternal iron excess. Human Reproduction, 15, 1843-8.

Little, M.P., Brocard, P., Elliott, P. and Steer, P.J. (2005). Hemoglobin concentration in pregnancy and perinatal mortality: a London-based cohort study. American Journal of Obstetrics and Gynecology, 193(1), 220-6.

McKenna, D., Spence, D., Haggan, S.E., McCrum, E., Dornan, J.C. and Lappin, T.R. (2003). A randomized tiral investigating an iron-rich natural mineral water as a prophylaxis against iron deficiency in pregnancy. Clinical and Laboratory Haematology, 25(2), 99-103.

Ross, M.G. and Idah, R. (2004). Correlation of maternal plasma volume and composition with amniotic fluid index in normal human pregnancy. Journal of Maternal - Fetal & Neonatal Medicine, 15,(2), 104-8.

Scholl, T.O. (2005). Iron status during pregnancy: setting the stage for mother and infant. American Journal of Clinical Nutrition, 81(5), 1218S-1222S.

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