What is the most tolerated oral iron supplement in pregnancy?

Most Tolerated Oral Iron Supplement in Pregnancy

Ferrous bisglycinate is the most tolerated oral iron supplement in pregnancy, with significantly fewer gastrointestinal side effects compared to ferrous fumarate and ferrous sulfate at equivalent doses. 1

Iron Supplementation in Pregnancy

Iron deficiency anemia is common during pregnancy, with an estimated prevalence of 18.6% among pregnant women in the United States 2. Adequate iron supplementation is essential for maternal health and optimal birth outcomes.

Types of Oral Iron Supplements

Several iron formulations are available for use during pregnancy:

1. Ferrous Bisglycinate

   • Most favorable gastrointestinal side effect profile
   • Associated with significantly fewer GI complaints
   • Lower frequency of black stools (8%) compared to other formulations 1

2. Ferrous Gluconate

   • Moderate GI side effect profile
   • May cause gastrointestinal discomfort, nausea, constipation or diarrhea 3

3. Ferrous Sulfate

   • Higher incidence of GI side effects
   • May cause gastrointestinal discomfort, nausea, constipation or diarrhea 4
   • Higher frequency of black stools (31%) 1

4. Iron(III) Polymaltose Complex

   • Superior safety profile compared to ferrous sulfate
   • Significantly fewer adverse events (29.3% vs 56.4%) 5

Dosing Recommendations

The U.S. Preventive Services Task Force and American College of Obstetricians and Gynecologists recommend:

• Prophylactic dosing: 30 mg of elemental iron per day in early pregnancy 2
• Treatment dosing: 60-120 mg of elemental iron per day for iron deficiency anemia 2

Tolerability Considerations

Gastrointestinal Side Effects

Low-dose iron supplementation appears to have fewer clinically significant GI side effects. In comparative studies:

• Ferrous bisglycinate (25 mg elemental iron) had significantly fewer GI complaints than ferrous fumarate (40 mg) and ferrous sulfate (50 mg) 1
• Iron(III) polymaltose complex showed fewer adverse events compared to ferrous sulfate (29.3% vs 56.4%) 5

Dosing Schedule

• Once-daily dosing of ferrous sulfate (65 mg elemental iron) is as effective as twice-daily dosing (130 mg elemental iron) with fewer side effects and better compliance 6

Clinical Algorithm for Iron Supplementation in Pregnancy

1. For prophylaxis in non-anemic pregnant women:

   • First choice: Ferrous bisglycinate (25 mg elemental iron daily)
   • Alternative: Iron(III) polymaltose complex (100 mg daily)

2. For treatment of iron deficiency anemia:

   • First choice: Ferrous bisglycinate (50-100 mg elemental iron daily)
   • Alternative: Iron(III) polymaltose complex (100 mg twice daily)
   • If these are unavailable: Ferrous sulfate or ferrous gluconate (60-120 mg elemental iron daily)

3. For women with significant GI intolerance to oral iron:

   • Consider switching to ferrous bisglycinate if not already using
   • Consider once-daily dosing instead of divided doses
   • If still not tolerated, consider IV iron supplementation 7

Important Considerations

• Do not take iron supplements within 2 hours of taking oral tetracycline antibiotics, as iron interferes with tetracycline absorption 3, 4
• Iron supplements may cause darkening of urine or stool, which is harmless but should be mentioned to patients to prevent unnecessary concern 3, 4
• Women on vegetarian diets may require almost twice as much iron due to lower absorption of non-heme iron 2

Monitoring

• Hemoglobin and serum ferritin should be monitored to assess response to treatment
• Serum ferritin has the highest sensitivity and specificity for diagnosing iron deficiency 7
• Continue supplementation until iron stores are replenished (ferritin >30 μg/L) 7

By selecting the most tolerable iron formulation and appropriate dosing strategy, clinicians can improve adherence to iron supplementation and effectively prevent or treat iron deficiency anemia during pregnancy.