Anemia of prematurity is a drop in red blood cells and hemoglobin that develops in the first weeks of life in babies born early. All newborns go through a natural dip in hemoglobin after birth, but in preterm babies it comes sooner, falls lower, and recovers more slowly. It is mainly caused by an immature erythropoietin response, made worse by frequent blood tests and low iron stores. Most babies need only careful monitoring and iron, while some need blood transfusions.
What Is Anemia of Prematurity?
Anemia means too few red blood cells, or too little hemoglobin, to carry oxygen efficiently. It is one of the most common hematological problems in the neonatal intensive care unit, and the earlier and smaller the baby, the more likely and more pronounced it is.
To understand it, it helps to know about physiologic anemia of infancy. In the womb, oxygen levels are low, so the fetus makes plenty of red cells. After birth, oxygen levels rise sharply, the body senses it has more than enough, and red cell production slows down. Hemoglobin gradually falls until the body again senses a need for more.
| Feature | Term infant | Preterm infant |
|---|---|---|
| Timing of hemoglobin low point | Around 8 to 12 weeks | Earlier, often 4 to 8 weeks |
| Typical lowest hemoglobin | About 9.5 to 11 g/dL | Lower, often 7 to 9 g/dL or below in the smallest babies |
| Red cell lifespan | Shorter than adult (adult is about 120 days) | Shorter still |
| Usual need for treatment | Rarely | Common, especially below 32 weeks |
Causes and Risk Factors
Low erythropoietin response
Erythropoietin (EPO) is the hormone that tells the bone marrow to make red cells. Before birth, the liver is the main source of EPO, and the liver is less sensitive to low oxygen than the kidney. The switch to kidney-based EPO production happens late in pregnancy, so babies born early produce less EPO than their degree of anemia would normally trigger.
Other contributing factors
- Blood sampling: small babies have a small total blood volume, so repeated tests remove a meaningful fraction of it.
- Shorter red cell survival: newborn red cells, which contain fetal hemoglobin, do not last as long as adult cells.
- Rapid growth: blood volume expands quickly as the baby gains weight, diluting the existing red cells.
- Low iron stores: most iron is transferred from mother to baby in the third trimester, which preterm babies miss.
- Illness: infection and inflammation can further suppress blood cell formation.
Signs and Symptoms
Many babies with anemia of prematurity show no obvious symptoms, which is why regular blood counts matter. When signs appear, they reflect the body working harder to deliver oxygen:
- Pale skin (pallor).
- Fast heart rate (tachycardia) or fast breathing (tachypnea).
- More frequent pauses in breathing (apnea) or drops in heart rate.
- Poor feeding, tiring during feeds, or slow weight gain.
- Lethargy or reduced activity.
- A rising need for supplemental oxygen.
These signs are not specific. Infection, lung disease, and other conditions can look similar, so the neonatal team interprets them alongside blood tests.
How It Is Diagnosed
Diagnosis relies on the complete blood count, tracking hemoglobin and hematocrit over time. A typical pattern in anemia of prematurity is a low hemoglobin with normal-sized red cells and an inappropriately low reticulocyte count, meaning the marrow is not responding as strongly as expected.
A key part of the diagnosis of anemia in any newborn is ruling out other causes. A high reticulocyte count or jaundice may suggest hemolysis, for example from blood group incompatibility. A sudden drop may point to bleeding. Small red cells suggest iron deficiency. Infection must always be considered in an unwell preterm baby.
Treatment and Management
Preventing blood loss
Prevention starts at delivery. Delayed cord clamping, waiting a short time before clamping the umbilical cord, lets extra blood flow from the placenta to the baby and boosts iron stores. In the unit, teams minimize blood draws, use small-volume sampling, and rely on non-invasive monitoring where possible.
Nutrition and iron
Adequate protein and calories support red cell production. Preterm babies are routinely given iron supplements, usually started within the first weeks once feeding is established, because their stores run out quickly. Adequate folate and vitamin B12 are also needed for healthy red cell production.
Red blood cell transfusion
Transfusion is the most direct treatment when anemia is significant or the baby is symptomatic. Neonatal units follow transfusion thresholds that depend on the baby’s age and how much respiratory support they need. Modern practice favors fairly restrictive thresholds to avoid unnecessary transfusions, while making sure sick babies are well supported. Small blood-volume aliquots from a single donor are often used to limit donor exposures.
Erythropoietin
Recombinant erythropoietin can stimulate red cell production and may reduce the number of transfusions some babies need. Its use varies between units, and it must be given with iron to be effective.
When to See a Doctor
After discharge, parents of a preterm baby should continue iron as prescribed and attend follow-up blood tests. Contact your baby’s doctor promptly if you notice:
- Increasing paleness, or pale lips and gums.
- Rapid breathing or a racing heartbeat at rest.
- Poor feeding, falling asleep during feeds, or weight loss.
- Unusual sleepiness or floppiness.
- Any pauses in breathing or color changes, which need emergency care.
Frequently Asked Questions
Will my premature baby grow out of anemia?
In most cases, yes. As the baby matures, erythropoietin production and red cell production pick up, and hemoglobin rises over the following months. Continuing iron supplements helps prevent later iron deficiency anemia.
Why does my baby need so many blood tests if they cause anemia?
Blood tests guide important decisions about breathing support, infection, nutrition, and jaundice. Teams try to take the smallest volumes possible and avoid tests that will not change care.
Are blood transfusions safe for premature babies?
Blood products are carefully screened and specially prepared for newborns. Like any treatment, transfusion has risks, which is why units use set thresholds and give transfusions only when the benefit is clear.
How long will my baby need iron drops?
Preterm babies commonly continue iron supplements for much of the first year, particularly if breastfed. Your pediatrician will advise on the dose and when to stop based on growth and blood tests.
