Iron In Pregnancy

Published on 27 January 2009 in Food, health and wellbeing

Introduction

Iron as an essential nutrient in pregnancy. What are the best sources, and how can we determine whether a pregnant woman has sufficient stores for optimal outcome?

We all know that iron is an important part of our red blood cells. It is contained in a molecule called haemoglobin, and is critical for carrying oxygen to all the cells of our body. However, iron is also an essential part of many other biological processes, including those that convert food into energy, and those that regulate development during pregnancy. It is clear, therefore, that an adequate supply of iron is paramount, especially in pregnancy..

In Scotland, iron is obtained from the diet from both meat and from green vegetables. Although haem iron, a major form of the iron in meat, is absorbed much better than non-haem iron, found in vegetables, the latter is the majority source of iron in most diets, mostly because of the small amount of meat in most diets. Iron from fortified cereals can also be a significant source. The World Health Organisation, however, tells us that iron deficiency is the most common nutritional problem in the world

The consequences of iron deficiency are not easy to determine. Once it becomes serious enough, an individual will become anaemic, but this occurs when stores are very low. Other processes can be affected in a more subtly way prior to the development of frank anaemia. Women, particularly those of child-bearing age, are much more likely than men to become anaemic, and even in Scotland, as many as 30 % of pregnant women are anaemic enough to require iron supplementation (Interestingly, many countries prescribe iron supplements to all pregnant women). Iron supplementation does not always work, and we need to understand more about how best to provide iron. We also need to learn what the consequences of deficiency are, for both the mother and her child, and can we reverse them?

Key Points

A pregnant woman needs an adequate store of iron at the beginning of pregnancy
Adequate dietary iron intake during pregnancy is very important during the whole of pregnancy
Iron deficiency during pregnancy can have effects on both the mother and her child
Some of these effects need to be recognised and, where possible, treatment initiated to reverse the effects as soon as possible
We need better indicators of iron status than currently used
We need to consider government recommendations for iron intake, and whether meat as an iron source is better than supplements

Research Undertaken

The effects of iron deficiency on pregnancy outcome have been investigated using animal models and the possible mechanisms underlying the phenotype (the set of symptoms) have been examined by scientists at the Rowett, in conjunction with collaborators in London, Nottingham. In rat models, iron deficiency results in increased perinatal death, in high blood pressure and increased obesity, which persist even into adulthood. Additionally, our collaborators in the USA have shown that there are marked changes in the brain which have significant consequences. There are also studies to show that these changes can be identified in babies born to mothers who are iron deficient.

In collaboration with scientists in Bristol, we have examined whether anaemia at the end of pregnancy in women is associated with the same changes in their offspring. In fact, we found the opposite – anaemia was actually associated with a small, but significant, drop in the blood pressure of the offspring. These findings were also observed by another group working in the USA. However, this group also demonstrated that anaemia early in pregnancy was associated with increased risk of premature birth and other pregnancy complications. They hypothesise that there are two causes of anaemia in the pregnant women. Anaemia in the first trimester is due to inadequate iron stores, and later in pregnancy occurs as blood volume expands (a normal physiological process). This theory actually agrees with our animal data.

Policy Implications

If the data are correct, there would seem to be a real possibility that maternal iron deficiency, especially early in pregnancy, has a deleterious effect on pregnancy outcome.

The policy implications relate to the way we analyse iron status in pregnancy and what we should recommend for women in pregnancy. There are better indicators of status than those currently used in most clinics. “Serum transferrin receptor” is widely used as a research biomarker for iron status, and we would recommend that studies were undertaken to examine how feasible it would be to introduce into the armoury of the hospital haematologist. With an accurate indicator of status, the obstetrician or midwife is in a better position to give informed advice.

The second aspect relates to dietary advice. Iron from meat is absorbed better than that from vegetables. Meat also contains a compound that can, under some circumstances, improve absorption of non-haem iron. Naively, therefore, one would presume that recommending an increase in meat intake would be a good idea. However, the implications for other aspects of health also need to be considered One clear point, which does need to be incorporated into the general advice given to any women, but especially to those considering becoming pregnant or at the early stages of pregnancy is that increasing iron intake, from whatever source, can only be beneficial

Author

Professor Harry J McArdle, Deputy Director (Science), Rowett Institute of Nutrition and Health, University of Aberdeen. h.mcardle@abdn.ac.uk

Topics

Food, health and wellbeing