This randomized controlled trial compares daily versus alternate-day oral iron supplementation in pregnant women with iron deficiency anemia during the second trimester. The study evaluates changes in hemoglobin and serum ferritin, treatment adherence, and gastrointestinal side effects to inform more patient-centered, physiologically aligned dosing strategies.

Iron deficiency anemia is the leading cause of anemia in pregnancy. Although daily oral iron is standard first-line therapy, it is frequently associated with gastrointestinal side effects and poor adherence. Because hepcidin rises after an iron dose and remains elevated for 24 to 48 hours, daily dosing may reduce fractional absorption; alternate-day dosing allows hepcidin to fall between doses, potentially improving absorption and tolerance.

This single-center, prospective, randomized, parallel-group trial will recruit pregnant women (13 to 27 weeks gestation) with hemoglobin below 11 g/dL and serum ferritin below 30 ng/mL from the antenatal clinic at PAF Teaching Hospital, Islamabad. Eligible, consenting participants will be randomized 1:1 to daily ferrous sulfate (one 325 mg tablet, approximately 65 mg elemental iron, once daily) or alternate-day ferrous sulfate (two 325 mg tablets, approximately 130 mg elemental iron, every other day) for four weeks.

The primary outcome is change in hemoglobin from baseline to Week 4. Secondary outcomes are change in serum ferritin, treatment adherence (proportion taking at least 80 percent of doses, by pill count and diary), and the frequency and severity of gastrointestinal side effects. Outcome assessors (laboratory personnel) are blinded to allocation; participant blinding is not feasible given the differing dosing schedules. Planned enrollment is 184 participants (92 per group), giving 90 percent power to detect a 0.40 g/dL difference in hemoglobin change at a two-sided alpha of 0.05, assuming a standard deviation of 0.83 g/dL.

Inclusion Criteria:

• Aged 18 to 40 years
• Pregnant women in the second trimester (13 to 27 weeks gestation)
• Hemoglobin below 11 g/dL with serum ferritin below 30 ng/mL
• Singleton pregnancy

Exclusion Criteria:

• Known congenital or acquired hemoglobin disorders (e.g., thalassemia, hemoglobinopathies)
• Chronic diseases affecting hemoglobin levels (e.g., chronic kidney disease, inflammatory disorders)
• Bleeding disorders or a history of frequent blood loss
• Gastrointestinal conditions impairing nutrient absorption (e.g., celiac disease or other malabsorption syndromes)
• Currently receiving parenteral iron
• Requiring blood transfusion

Participant and care-provider blinding is not feasible because the two arms follow visibly different dosing schedules. Outcome assessment is blinded: laboratory personnel analyzing hemoglobin and ferritin are masked to group allocation, with samples labeled by unique participant ID only.