Maternal-Fetal Medicine | Clinical Education

Iron Deficiency Anemia
in Pregnancy

Diagnosis • Implications • Evidence-Based Treatment

~40%

of pregnant women worldwide are anemic (WHO)

#1

most common nutritional deficiency in pregnancy

2–3×

increase in daily iron requirement during pregnancy

Diagnostic Thresholds

Hemoglobin cutoffs are trimester-specific to account for physiological hemodilution.

<11.0 g/dL

1st Trimester

<10.5 g/dL

2nd Trimester

<11.0 g/dL

3rd Trimester

2nd trimester threshold is lower due to maximum plasma volume expansion.

Iron Studies Workup

Ferritin is the most sensitive and specific marker for absolute iron deficiency.

IDA
<30 µg/L

Borderline
30–50 µg/L

Adequate
>50 µg/L

03050100+ µg/L

TSAT <20% — indicates iron-restricted erythropoiesis; useful when ferritin is falsely elevated by inflammation.

MCV <80 fL — microcytosis is a late finding; if low with normal iron stores, screen for hemoglobinopathy.

RDW >15% — elevated red cell distribution width; reactive thrombocytosis may also be present on CBC.

Maternal Implications

Cardiovascular

Exacerbates physiological tachycardia

Risk of high-output heart failure (severe IDA)

Peripartum

Increased risk of postpartum hemorrhage (PPH)

Higher susceptibility to peripartum infections

Increased likelihood of requiring blood transfusion

Psychosocial

Profound fatigue and impaired cognition

Increased rates of postpartum depression

Fetal & Neonatal Implications

🫀

Preterm delivery & premature rupture of membranes

⚖️

Low birth weight & fetal growth restriction (FGR)

🧠

Impaired neurodevelopment & long-term cognitive effects

🩸

Depleted fetal iron stores at birth → neonatal IDA

Cerebral iron deficit in early life has lasting behavioral and cognitive consequences.

Treatment: Nutritional Optimization

Prevention and maintenance — inadequate as monotherapy for established IDA.

Enhance Absorption

Heme iron (red meat, poultry, fish) — superior bioavailability

Vitamin C (ascorbic acid) with every iron-containing meal

Non-heme sources: leafy greens, legumes, fortified cereals

Avoid Inhibitors

Calcium / dairy products — consume 1–2 hrs apart

Tannins in tea and coffee — consume 1–2 hrs apart

Phytates in whole grains — separate from iron meals

Treatment: Oral Iron Therapy

First-line therapy for mild-to-moderate IDA (Hb 9.0–10.9 g/dL) diagnosed in the 1st or early 2nd trimester.

Dose: 40–80 mg elemental iron per dose

Alternate-day dosing — avoids 24–48 hr hepcidin surge; optimizes fractional absorption and reduces GI side effects

Take on an empty stomach with Vitamin C (e.g., orange juice) to maximize absorption

Limitations: GI adverse effects (constipation, nausea, epigastric pain) are common; requires 3–4 weeks for 1 g/dL Hb rise

Treatment: Intravenous Iron

Indications

Severe IDA (Hb <9.0 g/dL)

Diagnosis >30 weeks gestation

Oral iron intolerance or non-adherence

Malabsorption syndromes

Advantages

Rapid Hb normalization & full marrow iron repletion

Single-session dosing: up to 1000 mg in 15–30 min

Modern agents: ferric carboxymaltose, iron isomaltoside

Risks & Contraindications

Contraindicated in 1st trimester

Rare hypersensitivity / anaphylaxis

Hypophosphatemia (ferric carboxymaltose)

Treatment: Blood Transfusion

Reserved exclusively for severe, life-threatening scenarios.

Indications: Hb <7.0 g/dL with symptoms, hemodynamic instability, or active hemorrhage (abruption, previa)

Benefit: Immediate restoration of oxygen-carrying capacity

Critical limitation: Does not replete tissue iron stores — IV iron must follow once hemodynamically stable

Risks: Maternal alloimmunization (complicates future pregnancies), TACO, TRALI

Alloimmunization from transfusion can have permanent implications for subsequent pregnancies.

Treatment Modalities: At a Glance

Modality	Primary Indication	Key Advantage	Key Risk / Limitation
Nutrition	Prevention & maintenance	Safe; promotes holistic health	Inadequate for established IDA
Oral Iron	Mild–moderate IDA (1st/2nd tri)	Accessible, inexpensive, non-invasive	GI side effects; slow Hb response
IV Iron	Severe IDA or 3rd trimester	Rapid Hb normalization; repletes stores	Contraindicated 1st tri; facility needed
Transfusion	Hb <7.0 g/dL or hemodynamic instability	Immediate correction of tissue hypoxia	Alloimmunization; TACO/TRALI; no iron repletion

Clinical Summary

Screen all pregnant patients with CBC and ferritin; act on ferritin <30 µg/L — do not wait for Hb to fall.

Oral iron (alternate-day) is first-line for mild–moderate IDA in early pregnancy.

IV iron is standard of care after 14 weeks for severe IDA or late-pregnancy diagnosis.

Transfusion is a rescue therapy; always follow with IV iron to restore stores.

ACOG SMFM NICE Evidence-Based MFM Clinical Guidance

Iron Deficiency Anemiain Pregnancy