Anemia is one of the most common complications of pregnancy. Globally, about 37% of pregnant women are affected, which translates to roughly 32 million women at any given time. In the United States, the numbers are lower but still significant: nearly 1 in 5 pregnant women develops iron deficiency anemia specifically. Whether you’re newly pregnant or planning ahead, understanding why anemia happens during pregnancy, what it feels like, and what to do about it can make a real difference in how your pregnancy goes.
Why Pregnancy Makes Anemia So Common
Your blood volume increases by nearly 50% during pregnancy to support the growing placenta and fetus. But the liquid portion of your blood (plasma) expands faster than your red blood cell count, which dilutes the concentration of hemoglobin, the protein in red blood cells that carries oxygen. This natural dilution is sometimes called “physiologic anemia” because it’s an expected part of pregnancy, not a sign that something is wrong.
The problem starts when your body can’t keep up with the demand for new red blood cells. A growing fetus draws heavily on your iron stores, and iron is the essential building block of hemoglobin. If you entered pregnancy with low iron reserves or your diet doesn’t replace what the baby is using, the dilution effect tips from normal into true anemia. Iron deficiency is the most common pathologic cause. Other less frequent causes include folate deficiency, vitamin B12 deficiency, and inherited blood conditions like thalassemia or sickle cell disease.
Who Is Most at Risk
Some women enter pregnancy already at a disadvantage for maintaining healthy iron levels. You’re at greater risk if you:
- Had heavy menstrual periods before becoming pregnant, which depletes iron stores over time
- Have two pregnancies close together, leaving less time to rebuild reserves between births
- Are carrying more than one baby, since twins or triplets draw more iron from your supply
- Experience frequent vomiting from morning sickness, which limits how much iron you can absorb from food
- Don’t consume enough iron-rich foods, particularly if you follow a vegetarian or vegan diet without careful planning
Symptoms That Go Beyond Normal Fatigue
The tricky part about anemia during pregnancy is that its hallmark symptom, fatigue, is also one of the most universal experiences of pregnancy itself. Mild anemia often produces no noticeable symptoms at all, which is why routine blood work matters. As anemia worsens, though, the signs become more distinct from everyday pregnancy tiredness.
Watch for dizziness or lightheadedness, a noticeably fast heartbeat, shortness of breath during activities that didn’t used to wind you, and pale or dry skin that bruises easily. Some women develop a sore tongue or restless legs syndrome, an uncomfortable urge to move the legs that’s especially bothersome at night. Persistent headaches that don’t respond to rest or hydration can also be a clue. If you’re experiencing several of these together, it’s worth bringing them up at your next prenatal visit rather than assuming it’s just pregnancy wearing you down.
How Anemia Is Diagnosed in Each Trimester
Anemia is diagnosed through a simple blood test that measures your hemoglobin level, but the threshold for what counts as “anemic” actually shifts as your pregnancy progresses. The WHO defines anemia during the first and third trimesters as a hemoglobin level below 11.0 g/dL. During the second trimester, the cutoff drops slightly to 10.5 g/dL because that’s when plasma volume expansion peaks and some dilution is expected.
Most prenatal care includes a blood count at your first visit and again around 28 weeks. If your hemoglobin comes back low, your provider will typically run additional tests to figure out whether the cause is iron deficiency, a vitamin deficiency, or something else entirely. This distinction matters because the treatment differs depending on the underlying cause.
What Happens When Anemia Goes Untreated
Mild anemia during pregnancy is common enough that it sometimes gets brushed off, but the risks climb as severity increases. A large study published in JAMA Network Open found a clear relationship between how severe anemia was and how likely certain complications became.
For preterm birth, the risk increased modestly with mild anemia but rose more sharply with moderate and severe cases. The most striking finding involved severe postpartum hemorrhage, or heavy bleeding after delivery. Women with severe anemia were more than 15 times as likely to experience dangerous bleeding compared to women with normal hemoglobin levels. Even moderate anemia tripled the risk. This makes sense biologically: when your blood’s oxygen-carrying capacity is already compromised, your body is less equipped to handle the normal blood loss of childbirth.
Interestingly, the relationship between anemia and low birth weight is less straightforward. Some research suggests that mild anemia doesn’t increase the risk of having a smaller baby, and may even be associated with slightly lower risk compared to women with high-normal hemoglobin. The concern grows mainly with moderate to severe cases.
Prevention and Treatment
The Centers for Disease Control and Prevention recommends that all pregnant women take a low-dose iron supplement of 30 mg per day, regardless of whether they’re anemic. The American College of Obstetricians and Gynecologists similarly recommends universal low-dose iron supplementation during pregnancy, with the exception of women who have conditions like hemochromatosis that cause iron overload.
Most prenatal vitamins contain iron, but the amount varies by brand, so it’s worth checking the label. If you’re diagnosed with iron deficiency anemia, your provider will likely recommend a higher supplemental dose on top of your prenatal vitamin. Iron supplements are best absorbed on an empty stomach or with vitamin C (a glass of orange juice works), and they should be taken separately from calcium supplements or dairy, which interfere with absorption.
Side effects like constipation, nausea, and dark stools are common with iron supplements and lead many women to stop taking them. Splitting the dose, taking it every other day, or switching to a different formulation can help with tolerability. For women who can’t absorb oral iron well or who have severe anemia later in pregnancy, intravenous iron is an option that bypasses the digestive system entirely.
Iron-Rich Foods That Help
Supplements aside, dietary iron plays an important supporting role. Iron from animal sources (called heme iron) is absorbed roughly two to three times more efficiently than iron from plant sources. Red meat, poultry, and fish are the most concentrated sources. For plant-based diets, lentils, chickpeas, spinach, fortified cereals, and tofu all contribute, though you’ll absorb more if you pair them with a source of vitamin C like bell peppers, tomatoes, or citrus fruit.
Coffee and tea contain compounds that reduce iron absorption significantly, so spacing them at least an hour away from iron-rich meals or supplements makes a practical difference. Cooking in cast iron cookware also adds small but measurable amounts of iron to food, particularly with acidic dishes like tomato sauce.