Iron supplementation--is it necessary for healthy pregnancy?
Iron is an important mineral during pregnancy for both mother and fetus. Although the food supply provides numerous sources of iron, many women of child-bearing age in New Zealand consume intakes below what is recommended. The beneficial effects of iron supplementation in pregnancy on birth outcomes are controversial however maternal benefits have been clearly identified. The recommended dose for iron supplementation in pregnancy is generally accepted to be between 30-100 mg/day. Even when the women is aware of the importance of obtaining adequate dietary iron and are encouraged by midwives to follow healthy eating practices, iron supplementation may be indicated in some situations. Midwives should therefore assess women based on their iron status and history and provide appropriate advice regarding diet and supplementation to support healthy pregnancy.
Iron deficiency is the number one micronutrient deficiency worldwide with estimates of over two billion people affected. Iron deficiency is more common in women than men and its prevalence increases during pregnancy (Stoltzfus, 2001). Iron deficiency or iron depletion occurs when levels of stored iron in the body (ferritin) fall below normal levels (Table 1). As ferritin levels fall, the amount of iron transported in the blood also decreases resulting in a reduction in the amount of iron transported in the blood (transferrin saturation) and eventually a reduction in functional iron (haemoglobin). The reduction in haemoglobin indicates the presence of iron deficiency anaemia. Prophylactic iron supplementation during pregnancy is recommended in some countries (Danish National Board of Health, 1992; American College of Obstetricians and Gynecologists, 1993). In New Zealand routine iron supplementation for pregnancy is not recommended, instead supplementation is based on individual need. The following article provides an overview of iron in pregnancy and explores strategies for attaining adequate iron status focusing on iron supplementation for at-risk groups.
The role of iron in pregnancy
Iron is a component of haemoglobin, which is required during pregnancy to supply maternal and fetal tissues with oxygen. In pregnancy additional haemoglobin is required for the increase in maternal red cell mass and to allow for normal blood losses at delivery. An insufficient haemoglobin concentration may cause fatigue, reduced immune function, deficits in concentration and mood, and impaired work performance (Bodnar, Cogswell & McDonald, 2005). Further, a reduction in haemoglobin during pregnancy has been associated with increased risk for post-partum haemorrhage and overall maternal morbidity (Allen & Casterline-Sabel, 2000).
Fetal and infant effects
Low maternal haemoglobin has been associated with an increased risk of pre-term birth, low birth weight and perinatal mortality particularly in developing countries where rates of anaemia are high and other factors such as general hygiene and nutrition are sub-optimal (Rasmussen, 2001; Yip, 2000). Infants born to iron-deficient or anaemic mothers are at greater risk of being iron-deficient or anaemic (Haram, Nilsen & Ulvik, 2001). However, in a group of New Zealand infants this relationship was not evident (Emery & Barry, 2004). Iron-deficiency and iron-deficiency anaemia in infancy has also been linked to poor cognition and reduced immunity (Booth & Aukett, 1997).
Assessment of iron status
There is controversy with respect to the appropriate cut-off values for defining iron deficiency and iron-deficiency anaemia particularly for pregnancy. The World Health Organisation defines anaemia as haemoglobin levels below 110 g/L in the first and third trimester and below 105 g/L in second trimester. Milman, Bergholt, Eriksen, Byg, Graudal, Pedersen & Hertz (2005) suggest similar cut-offs but also include that ferritin levels below 12 micrograms/ L is indicative of iron-deficiency anaemia. The Australian Iron Advisory Panel (no date [n.d.]) recommends using haemoglobin and ferritin along with a variety of risk factors including a history of iron deficiency, post-partum haemorrhage, recent blood donation, poor socioeconomic status and heavy menses, to assess a woman's risk of iron deficiency and iron deficiency anaemia in pregnancy. They suggest that woman in the first trimester of pregnancy with haemoglobin levels between 105-115 g/L and one or more risk factors are at risk of developing iron deficiency in pregnancy whereas women with haemoglobin less than 105 g/L are considered anaemic.
Iron recommendations for pregnancy
The New Zealand recommendation for iron intake during pregnancy is 27 mg/day for both adolescents (14-18 years) and women (>18 years) (Australian Government National Health and Medical Research Council, 2005). Little is known about the iron intake and iron status of pregnant New Zealand women. However according to the 1997 National Nutrition Survey, non-pregnant women aged 25-44 had mean iron intakes of only 10.5 mg/day (Russell, Parnell & Wilson, 1999). Although women in this survey had low intakes of iron, the prevalence of iron deficiency anaemia in this population was low (2%). There is no evidence to suggest that dietary intakes of pregnant women are significantly different than non-pregnant women therefore it is likely that pregnant New Zealand women also have low intakes of dietary iron, well below the recommendations. Iron absorption, however is enhanced in pregnancy; the mechanism by which this occurs is not known (Fairbanks, 1999). Despite enhanced iron absorption in pregnancy, women with low dietary iron intakes prior to and during pregnancy, are at increased risk for iron deficiency or iron deficiency anaemia in pregnancy.
How to ensure adequate iron status
Iron has many oxidation states, however only the ferric and ferrous states exist in food. When describing the iron present in food the terms haem and non-haem are used. Both haem and non-haem iron are present in animal products, whereas plant sources such as whole grains, nuts, beans and legumes contain only non-haem iron. Haem iron is present as ferrous iron, bound within haemoglobin and myoglobin in animal flesh. Non-haem iron is found in foods as ferric and ferrous iron (Groff & Gropper, 2000). Some foods in New Zealand are also fortified with non-haem iron including breakfast cereals, sweet biscuits and some milks.
Only a small proportion of dietary iron is absorbed in the gut and therefore, not all dietary iron consumed is available for use by the body. This is referred to as the bioavailability of iron. Haem iron is readily absorbed by the body whereas non-haem iron is less soluble in the gut and therefore less is absorbed. Up to one-third of haem iron and 220% of non-haem iron is considered bioavailable (Hurrell, 1997). To enhance the bioavailability of non-haem iron the following strategies can be employed:
* Consumption of vitamin C rich food with meals or snacks containing iron (examples of vitamin C rich foods include tomatoes, capsicums, strawberries). Vitamin C increases the bioavailability of iron by forming a chelate with iron converting ferric iron into ferrous iron, a more soluble and absorbable form of iron (Cook, 2001).
* Consuming small portions of meat, poultry and fish with foods containing non-haem iron (examples might include bean chilli with small portions of mince beef, vegetable and nut stir-fry with small quantities of chicken, beef or pork). Certain amino acids present in high concentrations in animal flesh enable the conversion of ferric iron to the ferrous form (Hurrell, 1997).
* Consuming black types of tea (oolong, Ceylon) one to two hours before or after a meal rather than with a meal. Tannins, polyphenolic co pounds present in tea, bind to iron in the gut thereby inhibiting the absorption of iron (ibid).
Furthermore, zinc and calcium can interfere with iron absorption thereby reducing iron bioavailability. Zinc, calcium and iron compete for absorption into the intestinal mucosa; however this interaction appears to occur only when these minerals are given in high doses such as those found in supplements. Calcium and zinc present within food do not appear to have similar inhibitory effects on iron absorption (Minihane & Fairweather-Tait, 1998; Groff & Gropper, 2000).
In addition to food, iron supplements can also be used to meet dietary iron requirements. There are many types of iron supplements available in New Zealand (Table 2). Iron supplements come as either tablets or liquid, and are available in various doses ranging from tonics with negligible amounts (<10mg), to low-dose (20-60mg), slow-release and high-dose (>60mg). Iron supplements contain ferrous iron and are combined with other compounds such as fumurate, gluconate, lactate or sulphate to increase its stability. The term 'elemental iron' is used to indicate the amount of iron present within these compounds, and therefore represents the amount of iron available for absorption.
The need for iron supplementation is greatest for women who enter pregnancy with poor iron status. Poor iron status may be attributed to a variety of factors including a poor diet with low intake of iron-rich foods, history of iron-deficiency or iron-deficiency anaemia, recent pregnancy, previous post-partum haemorrhage and low socioeconomic status (Australian Iron Advisory Panel, n.d.). In addition, women with high menstrual loss are also at risk for iron deficiency and iron deficiency anaemia (Lynch, 2000).
Adolescents, who often have sub-optimal intakes of iron and low blood ferritin concentrations, are also at increased risk for developing iron-deficiency anaemia in pregnancy (ibid). Non-pregnant New Zealand adolescents aged 15-18 years, have iron intakes of 10.4 mg/day (Russell et al, 1999) well below the recommended intakes of 15 mg/day (Australian Government National Health and Medical Research Council, 2005).
Although dietary strategies should be encouraged to improve iron status, increasing dietary iron intake alone does not always result in increased haematological values in the short term. A study of non-pregnant New Zealand women with mild iron deficiency who had made significant dietary changes over four months achieved minimal increases in iron status, compared to those supplemented daily with 50 mg elemental iron (Heath, Skeaff, O'Brien, Williams & Gibson, 2001). Therefore in some situations, particularly in at-risk groups as described, iron supplementation is warranted.
Low-dose iron supplementation in pregnant women with haemoglobin levels of 110-120 g/L has been found to be effective in preventing iron deficiency and iron-deficiency anaemia. Supplementation with 20 mg elemental iron/day 20 weeks gestation until delivery prevented iron deficiency and iron-deficiency anaemia in a group of Australian women (Makrides, Crowther, Gibson, Gibson & Skeaff, 2003). Milman et al (2005) also found that daily supplementation of 40 mg elemental iron early in pregnancy (18 weeks gestation) was as effective as 60 or 80 mg elemental iron/day in preventing iron deficiency and iron deficiency anaemia in women with an initial mean haemoglobin of 117 g/L. Similarly, daily supplementation of 50 mg elemental iron from 21-26 weeks gestation for three months resulted in a mean rise in haemoglobin, from 112 g/L to 123 g/L (Ekstrom, Kavishe, Habicht, Frongillo, Rassmussen & Hemed, 1996). Cogswell, Parvanta, Ickes, Yip & Brittenham (2003) however, found that daily supplementation of 30 mg elemental iron from 10 weeks gestation until 28 weeks gestation did not result in a lower prevalence of iron-deficiency anaemia compared to placebo in a group of iron replete, non-anaemic women. It is possible however, that if supplementation continued throughout pregnancy a lower prevalence of iron-deficiency anaemia may have been found. These studies demonstrate that low-dose iron supplementation (<60 mg/day) can help prevent iron deficiency anaemia in women with haemoglobin values at the lower end of normal when given from approximately 20 weeks gestation until birth.
Although low-dose iron supplementation can be effective in preventing iron-deficiency and iron-deficiency anaemia, higher levels are necessary for treatment. A meta-analyses of data from randomized controlled trials between 1966 and 1998 found that >90 mg iron/day was needed to improve haematological indices in pregnant, anaemic women (Sloan, Jordan & Winikoff, 2002).
Some of the issues regarding iron supplementation are tolerance and compliance. Gastro-intestinal side effects such as nausea, vomiting, epigastric pain and constipation are associated with iron supplementation. However, the results of many studies, including a large (n=427) randomised controlled trial, found that gastro-intestinal side effects associated with iron supplementation did not differ between women supplemented daily with 20, 40, 60 or 80 mg elemental iron in the form of ferrous fumarate (Milman, Byg, Bergholt & Erikson, 2006). Higher doses of elemental iron (>100 mg) however, have been reported to increase side effects and therefore are associated with lower compliance than lower doses (Ekstrom et al, 1996). There is limited evidence to support the use of one type of iron supplement over another due to tolerance; however larger doses irrespective of type tend to be less tolerable than low dose supplements.
When using supplements, toxicity issues should always be addressed. With iron however, toxicity is generally not a concern as the body regulates iron absorption based on stored levels (ferritin). Therefore individuals with poor stores have a greater absorptive ability than those with normal stores. There are some women for whom iron supplementation is contraindicated. Women with the condition haemochromatosis, a condition most common in individuals of Northern European descent, have an enhanced ability to absorb and store iron in the body. The increase in body iron, if not treated, results in iron overload and leads to tissue damage, specifically in the liver and heart (Groff & Gropper, 2000).
Despite the controversy surrounding the benefits of iron supplementation for birth outcome, benefits to maternal haematological values and general well-being are well established. It is important for pregnant women to maintain healthy iron levels for both themselves and their offspring. It is essential therefore, that iron status be monitored throughout pregnancy, and that midwives provide necessary recommendations regarding diet and supplementation. Even when supplementation is warranted, strategies to increase a woman's dietary iron intake are paramount for developing good eating habits that will continue throughout pregnancy and beyond.
Accepted for publication: March 2007.
Allen, H. L., & Casterline-Sabel, J. (2000). Prevalence and causes of nutritional anaemia. In U. Ramakrishnan (Ed.). Nutritional anemias. Florida: CRC Press.
American College of Obstetricians and Gynecologists (1993). Nutrition during pregnancy: ACOG Technical Bulletin No. 179. Washington DC: ACOG.
Australian Government National Health and Medical Research Council. (2005). Nutrient Reference Values for Australia and New Zealand including Recommended Dietary Intakes. Australia: National Health and Medical Research Council.
Australian Iron Advisory Panel (n.d.). Iron and pregnancy recommended guidelines. Accessed September 1, 2006, from http://www.ironpanel.org.au/AIS/AISdocs/pregdocs/ pregtitle.html
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Cogswell, M. E., Parvanta, I., Ickes, L., Yip, R., & Brittenham, G. M. (2003). Iron supplementation during pregnancy, anemia, and birth weight: a randomized control trial. American Journal of Clinical Nutrition 78, 773-781.
Cook, J. D., & Reddy, M. B. (2001). Effect of ascorbic acid intake on nonheme-iron absorption from a complete diet. American Journal of Clinical Nutrition 73, 93-98.
Danish National Board of Health. (1992). Recommendations about iron supplementation during pregnancy Ugeskr Laeger 154, 3445.
Ekstrom, E. M., Kavishe, F. P., Habicht, J., Frongillo, E. A., Rusmussen, K. M., & Hemed, L. (1996). Adherence to iron supplementation during pregnancy in Tanzania: determinants and hematologic consequences. American Journal of Clinical Nutrition 64, 368-74.
Emery, D., & Barry, D. (2004). Comparison of Maori and non-Maori maternal and fetal iron parameters. The New Zealand Medical Journal 117, 909-913.
Fairbanks, V. F. (1999). Iron in medicine and nutrition. In M. E. Shils, J. A. Olson, M. Shike, & A. C. Ross (Eds.) Modern nutrition and disease (9th ed.). Baltimore: Williams & Wilkins.
Groff, J. L., & Gropper, S. S. (2000). Advanced nutrition and human metabolism (3rd ed.). Belmont, California: Wadsworth Thomson Learning.
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Makrides, M., Crowther, C. A., Gibson, R. A., Gibson, R. S., & Skeaff, C. M. (2003). Efficacy and tolerability of low-dose iron supplements during pregnancy: a randomized controlled trial. American Journal of Clinical Nutrition 78, 145-153.
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Strategies to ensure optimal iron status for pregnancy
* Consume iron rich foods on a daily basis
* Increase the bioavailability of iron in foods by
** Consuming foods rich in vitamin C
** Consuming small portions of meat, poultry and fish with foods containing non-haem iron
** Avoiding black types of tea (oolong, Ceylon) with meals
* Consider the use of iron supplements (40-60 mg elemental iron/day) for women with poor iron status and take at separate times of day than calcium or zinc supplements.
Sandra Elias is a Senior Lecturer in the School of Midwifery, Otago Polytechnic in Dunedin. She completed an MSc in the area of Maternal Nutrition from the University of British Columbia, Canada.
Contact for correspondence: Email: firstname.lastname@example.org
Table 1. Parameters of iron status used in iron assessment Iron status stored iron Transport iron (ferritin) (transferrin) Iron-deficiency anemia Low Low Iron depletion Low Normal Normal iron status Normal Normal Iron overload High High Iron status Functional iron (haemoglobin) Iron-deficiency anemia Low Iron depletion Normal Normal iron status Normal Iron overload Normal Table 2. Iron supplements available in New Zealand Supplement name Preparation Bayer Elevit ferrous fumurate Blackmore Pregnancy and Breastfeeding ferrous fumurate Ferrit Ferroforce ferrous lactate Abbott Ferro-gradumet ferrous sulphate Abbott Ferrograd-folic ferrous sulphate Healtleries Iron with Vitamin C ferrous gluconate Healtheries Iron Fizz with Vitamin C iron oxide Red Seal Floravital tonic ferrous gluconate Solgar Gentle Iron iron bisglycinate (chelated iron) Solgar Prenatal Nutrients iron bisglycinate (chelated iron) Thompsons Liquid Iron ferrous gluconate Thompsons Organic Iron Complete ferrous fumurate Thompsons Prenagcare ferrous fumurate Supplement name Daily Amount of Subsidised DOse elemental by iron per Pharma daily dose (mg) Bayer Elevit 1 tablet 60 No Blackmore Pregnancy and Breastfeeding 2 tablets 5 No Ferrit Ferroforce 15 ml 15 No Abbott Ferro-gradumet 1 tablet 105 Partsubshfy Abbott Ferrograd-folic 1 tablet 105 Partsubsicy Healtleries Iron with Vitamin C 1 tablet 20 Yes Healtheries Iron Fizz with Vitamin C 2 tablets 12 No Red Seal Floravital tonic 20 mls 19 No Solgar Gentle Iron 1 tablet 25 No Solgar Prenatal Nutrients 1 tablets 27 No Thompsons Liquid Iron 10 mls 20 No Thompsons Organic Iron Complete 1 tablet 24 No Thompsons Pregnacare 2 tablets 10 No
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