Anemia in pregnancy is a condition where your blood doesn’t carry enough oxygen to your body and your baby, most often because of low iron levels. It’s diagnosed when hemoglobin drops below 11 g/dL in the first and third trimesters, or below 10.5 g/dL in the second trimester. Some degree of blood dilution is completely normal during pregnancy, but true anemia goes beyond that natural shift and can affect both your health and your baby’s development.
Why Pregnancy Changes Your Blood
Your body undergoes a dramatic blood expansion during pregnancy. Total blood volume increases by roughly 45% above pre-pregnancy levels, with some women seeing increases as high as 100%. Red blood cell production also ramps up, increasing by about 40%, but plasma volume grows faster. The result is a natural dilution effect: your blood literally becomes thinner because there’s proportionally more fluid than red blood cells.
This “physiological anemia” is expected and usually harmless. Hemoglobin levels around 11 g/dL from hemodilution alone are considered normal. The problem starts when iron stores can’t keep up with the increased demand for red blood cell production, and hemoglobin falls below the thresholds for your trimester. At that point, the dilution is no longer doing most of the work. Your body genuinely lacks the raw materials to carry oxygen efficiently.
Iron Deficiency Is the Main Cause
Iron deficiency accounts for the vast majority of anemia cases in pregnancy. Your body needs iron to make hemoglobin, and during pregnancy, iron demands roughly double because you’re building extra blood volume, growing a placenta, and supporting a developing baby. If you entered pregnancy with low iron stores, or if your diet doesn’t supply enough, deficiency develops quickly.
A ferritin level below 30 µg/L in a pregnant woman indicates iron deficiency, even if hemoglobin hasn’t dropped yet. This is a lower threshold than many people realize. Ferritin measures your stored iron, so it falls before hemoglobin does. By the time your hemoglobin is officially “anemic,” your iron reserves have often been depleted for weeks.
Less commonly, anemia during pregnancy results from folate or vitamin B12 deficiency. Both nutrients are essential for producing healthy red blood cells, and deficiency in either can cause a type of anemia where red blood cells are abnormally large and don’t function properly. Folate deficiency also carries the additional risk of neural tube defects in the baby, which is why prenatal vitamins contain folic acid.
Who Is at Higher Risk
Certain factors make anemia more likely. Carrying twins or multiples increases iron demand significantly. Short intervals between pregnancies don’t give your body enough time to rebuild iron stores. Adolescent pregnancies carry higher risk because the mother’s own body is still growing. Heavy periods before pregnancy, a history of anemia, or a diet low in iron-rich foods (particularly plant-based diets without careful planning) also raise the odds.
Morning sickness compounds the problem. If nausea or vomiting limits what you can eat during the first trimester, iron intake drops at the exact moment your blood volume starts expanding.
Symptoms That Go Beyond Normal Fatigue
The tricky part of recognizing anemia in pregnancy is that its earliest symptom, fatigue, is also one of the most universal pregnancy complaints. Mild anemia often produces no noticeable symptoms at all. As it progresses, though, certain signs become harder to dismiss.
Shortness of breath with light activity, dizziness or feeling faint when you stand up, a noticeably fast heartbeat, and feeling cold when others around you are comfortable all point toward anemia rather than typical pregnancy tiredness. Pale or dry skin, easy bruising, headaches, a sore tongue, and restless legs syndrome (an uncomfortable urge to move your legs, especially at night) are additional signs. Some women develop pica, an unusual craving to chew ice or other non-food items, which is a surprisingly reliable indicator of iron deficiency.
Severe anemia can cause low blood pressure, trouble concentrating, and a heartbeat that feels pounding or irregular. If you notice several of these symptoms together, it’s worth mentioning at your next prenatal visit rather than assuming it’s just pregnancy wearing you down.
Risks for You and Your Baby
Untreated anemia isn’t just about feeling tired. It carries measurable risks for both mother and child, and the more severe the anemia, the steeper those risks climb.
For mothers, the most significant concern is postpartum hemorrhage, or excessive bleeding after delivery. Data from a large clinical trial found that 6.2% of women with moderate anemia experienced postpartum hemorrhage, compared to 11.2% of women with severe anemia. For every 10 g/L drop in hemoglobin before birth, the odds of significant bleeding after delivery increased by about 29%. This matters because a woman who is already anemic has less capacity to tolerate blood loss.
For babies, iron deficiency during pregnancy is linked to low birth weight, premature delivery, and restricted growth in the womb. Perhaps less obvious is the long-term effect on the baby’s own iron stores. Children born to iron-deficient mothers tend to have lower iron levels at 9 months of age, putting them at greater risk of developmental delays associated with infant iron deficiency.
How It’s Diagnosed
Anemia screening is part of routine prenatal care. A standard blood test checks your hemoglobin and hematocrit (the percentage of your blood made up of red cells). The diagnostic thresholds shift slightly by trimester to account for normal blood dilution:
- First trimester: hemoglobin below 11 g/dL or hematocrit below 33%
- Second trimester: hemoglobin below 10.5 g/dL or hematocrit below 32%
- Third trimester: hemoglobin below 11 g/dL or hematocrit below 33%
If your hemoglobin is low, your provider will typically check ferritin to confirm whether iron deficiency is the cause. A ferritin below 30 µg/L confirms depleted iron stores. Some practitioners also test iron saturation levels and iron-binding capacity, which can reveal functional iron deficiency even when ferritin appears borderline normal.
Treatment: Oral and IV Iron
The CDC recommends that all pregnant women take a low-dose iron supplement of 30 mg per day starting at their first prenatal visit as a preventive measure. Most prenatal vitamins contain this amount. If anemia is already present, the treatment dose increases to 60 to 120 mg of elemental iron per day.
Oral iron supplements work well for many women but come with common side effects: constipation, nausea, and stomach cramps. Taking iron with a small amount of food (though not with dairy or calcium supplements, which block absorption) and pairing it with vitamin C can help both tolerance and absorption. Even with consistent daily use, it takes several weeks for hemoglobin levels to noticeably improve.
When oral iron doesn’t work, either because side effects make it impossible to take consistently or because absorption is poor, intravenous (IV) iron is the next step. IV iron is considered safe starting in the second trimester and can replenish stores much faster than oral supplements. Some practitioners now advocate for checking iron markers in all pregnant patients and offering IV iron earlier rather than waiting for oral therapy to fail, particularly for women diagnosed late in pregnancy who have limited time before delivery to rebuild their levels.
For anemia caused by folate or B12 deficiency, supplementation with the specific missing nutrient is the treatment. Folate supplementation is standard in prenatal care (typically 400 to 800 micrograms of folic acid daily), which is one reason folate-deficiency anemia is less common than iron deficiency in populations with access to prenatal vitamins.
Improving Iron Through Food
Supplements aside, dietary iron plays an important supporting role. Iron from animal sources (red meat, poultry, fish) is absorbed roughly two to three times more efficiently than iron from plant sources (beans, lentils, spinach, fortified cereals). If you eat a plant-based diet, combining iron-rich foods with vitamin C sources like citrus, bell peppers, or tomatoes significantly boosts absorption.
Coffee, tea, and calcium-rich foods compete with iron for absorption, so spacing these away from iron-rich meals or supplements by an hour or two makes a practical difference. This is a small adjustment that adds up over the course of a pregnancy.