Evaluating iron supplements during pregnancy - Maternal Nutrition

Nutrition Research Newsletter, August, 2003

Iron deficiency (ID) is one of the risks to pregnant women. Causes of ID include extra iron required by the growing fetus and the placenta and the increased maternal red cell mass.

The potential risks of iron deficiency anemia (IDA) to pregnant women are increased fatigue and decreased work performance; cardiovascular stress due to inadequate hemoglobin and low oxygen saturation; impaired resistance to infection; and poor tolerance to heavy blood loss and surgical interventions at delivery. Currently, in countries such as Australia, New Zealand, the UK, and Canada, iron supplementation is not recommended during pregnancy. However, in other nations, such as in the United States and France, iron supplementation during pregnancy is standard practice. The evidence for either a beneficial or harmful effect of iron supplementation on pregnancy outcomes is inconclusive.

A study was performed in Australia to assess the effect of iron supplementation at a level (20 mg/d) that would ensure that most women in the intervention group at least met the RDI. Primary outcomes were the incidence of maternal IDA at delivery, maternal iron status at 6 months postpartum, and gastrointestinal side effects at 24 and 36 weeks of gestation. Secondary outcomes were the proportion of women requiring high-dose iron treatment during pregnancy, maternal indexes of well-being as measured by a self-administered questionnaire at 36 weeks of gestation and at 6 weeks and 6 months postpartum, and maternal serum zinc status at delivery and at 6 months postpartum.

Subjects included women having singleton or twin pregnancies. Active supplements were ferrous sulfate tablets, each containing 20 mg elemental iron. Placebo tables were identical in color, size, and shape. Women were asked to take on tablet daily between meals from week 20 of gestation until delivery. Monthly telephone calls were made to encourage compliance and assess the average number of tablets not taken during the previous month. If anemia was detected in the routine 28-week blood sample or if the woman's clinician considered her hemoglobin concentration to be too low, the woman was advised to purchase and take a high-dose iron supplement (containing = 80 mg/tablet) until the end of pregnancy.

A total of 430 women enrolled in the study and 386 completed the follow-up to 6 months postpartum. At the time of delivery, fewer women from the iron-supplemented group than from the placebo group had IDA [6/198, or 3%, compared with 20/185, or 11%; relative risk (RR): 0.28; 95% CI 0.12, 0.68; P < 0.005], and fewer women from the iron-supplemented group had ID (65/186, or 35%, compared with 102/176, or 58%; RR: 0.60; 95% CI: 0.48, 0.76; P < 0.001). There was no significant difference in gastrointestinal side effects between the placebo and supplemented groups. At 6 months postpartum, fewer women from the iron-supplemented group had ID (31/190, or 16%, compared with 51/177, or 29%; RR: 0.57; 95% CI: 0.38, 0.84; P < 0.005). The rate of IDA between the groups did not differ significantly at 6 months postpartum.

This study suggests that supplementing the diet of pregnant women with 20 mg iron per day from week 20 until delivery is an effective strategy for preventing both IDA and ID without significant side effects.

M. Makrides, C. Crowther; R. Gibson, et al. Efficacy and tolerability, of low-dose iron supplements during pregnancy: a randomized controlled trial. Am J Clin Nutr; 78:145-153 (July 2003). [Correspondence: M Makrides, Child Nutrition Research Centre, Level 1, Clarence Rieger Building, Women's and Children's Hospital 72 King William Road, North Adelaide SA 5006, Australia. E-mail: makridesm@mail.wch.sa.gox.au].