Should we lower the dose of iron when treating anaemia in pregnancy? A randomized dose-response trial

To compare the efficacy and side effects of low-dose vs high-dose iron supplements to correct anaemia in pregnancy.

One hundred and eighty women with anaemia (haemoglobin <110 g l(-1)) in mid-pregnancy. The women were randomly allocated to 20; 40 or 80 mg of iron daily for 8 weeks from mid-pregnancy.

One hundred and seventy-nine (99%) women completed the trial. At the end of treatment, there was a clear dose-response of increasing mean haemoglobin concentration with iron dose (111+/-13 g l(-1) at 20 mg per day, 114+/-11 g l(-1) at 40 mg per day and 119+/-12 g l(-1) at 80 mg per day, P=0.006). However, the incidence of anaemia did not differ statistically between groups. Compared with women in the 80 mg iron group, the odds ratio of anaemia was 1.9 (95% CI: 0.8, 4.3, P=0.130) and 1.1 (95% CI: 0.5, 2.6, P=0.827), respectively, for women in the 20 mg iron group and the 40 mg iron group. The incidence of gastrointestinal side effects was significantly lower for women in the 20 mg iron group compared with women in the 80 mg iron group; the odds ratio was 0.4 (95% CI: 0.2, 0.8, P=0.014) for nausea, 0.3 (95% CI: 0.2, 0.7, P=0.005) for stomach pain and 0.4 (95% CI: 0.2, 0.9, P=0.023) for vomiting.

Low-dose iron supplements may be effective at treating anaemia in pregnancy with less gastrointestinal side effects compared with high-dose supplements.