Pregnancy roughly doubles a woman's iron requirement. The plasma volume expands, the placenta and foetus are accumulating iron, and lactation that follows continues the demand. The recommended daily intake rises from 18 mg to 27 mg, and the total demand across the full pregnancy is roughly 1000 mg of additional iron. Almost no patient meets this from diet alone.
What standard prenatal vitamins provide
Most prenatal multivitamins contain 27 to 30 mg of elemental iron — enough for patients who start pregnancy with replete stores and who absorb oral iron well. For patients who begin pregnancy already iron-depleted (a large fraction, given that many enter pregnancy with low ferritin from menstrual losses or prior pregnancies), the standard prenatal is not enough.
Compounding the issue: many women experience nausea in the first trimester and abandon their prenatal vitamins for weeks at a time. Absorption is also poor in some patients regardless of dose.
When to test
A reasonable structure:
- First trimester: baseline CBC and ferritin at the booking visit.
- 28 weeks: repeat CBC and ferritin. This is the point when foetal iron demand peaks and many patients first show deficiency.
- Earlier or more often in patients with prior iron deficiency, multiple gestation, or symptoms.
A ferritin below 30 ng/mL in pregnancy warrants attention. Many obstetric guidelines now treat at this threshold rather than waiting for haemoglobin to fall.
Oral iron — start here, but expect limits
Oral iron remains first-line in early pregnancy:
- Ferrous fumarate, ferrous sulphate, ferrous gluconate — standard options
- Heme iron polypeptide or alternate-day dosing schedules can be considered for poor tolerance
- Vitamin C with the dose improves absorption
The challenges are real: nausea, constipation, abdominal discomfort, and a metallic taste are common reasons for discontinuation. When patients cannot tolerate oral iron, or when oral iron has failed to raise ferritin after a reasonable trial, the conversation moves to IV.
IV iron in pregnancy
Intravenous iron is considered safe in pregnancy after the first trimester. The most commonly used agents in Canada (ferric derisomaltose / Monoferric, ferric carboxymaltose / Ferinject) have substantial safety data in pregnancy and replete stores quickly — usually within a few weeks of infusion. The benefit is meaningful: fewer transfusions at delivery, lower rates of post-partum anaemia, less maternal exhaustion in the early weeks with the baby.
IV iron is particularly worth considering when:
- Oral iron has failed or is not tolerated
- The pregnancy is in the third trimester and time is short before delivery
- Baseline ferritin is severely low
- The patient has a high-risk delivery planned (e.g., expected blood loss)
Post-partum — the missed window
The post-partum period combines two sources of iron loss: delivery blood loss (often 500 mL or more) plus the demands of lactation. Symptoms of post-partum iron deficiency — exhaustion, brain fog, low mood, hair shedding — blend seamlessly with normal new-parent fatigue, and are rarely distinguished without specific testing.
A 6-week post-partum CBC plus ferritin catches most cases. Treatment in this window is straightforward and often dramatic in its effect — patients who thought they had post-partum depression sometimes discover their fatigue was iron all along.
When to refer
- Confirmed deficiency not responding to oral iron
- Significant deficiency in late pregnancy, with limited time to correct it
- Post-partum patients with consistent symptoms and low ferritin
- Patients with prior post-partum anaemia in a previous pregnancy
Our Iron Infusion Clinic works in close coordination with obstetricians and family physicians. Most referred patients are seen within the same week, with IV iron available on-site when indicated.