Last Updated on November 20, 2025 by Ugurkan Demir
Physiological anemia is a common condition during pregnancy. When a woman is pregnant, her body changes a lot to help the growing baby. One major change is the increase in blood volume, which leads to hemodilution or dilutional anemia.
The World Health Organization (WHO) reports that about 37–40% of pregnant women worldwide have anemia. Most of this is due to the body’s natural changes, not a lack of iron.
This condition is a normal part of pregnancy. It happens because the body makes more plasma than red blood cells. Even though it might sound concerning, physiological anemia is usually not dangerous—it’s just the body’s way of adapting to pregnancy needs.
Key Takeaways
- Pregnancy causes an increase in blood volume, leading to hemodilution.
- Hemodilution is a normal adaptation to pregnancy.
- Approximately 37-40% of pregnant women globally suffer from anemia.
- Physiological changes, not just iron deficiency, contribute to anemia in pregnancy.
- Liv Hospital offers expert care for managing pregnancy-related conditions.
What Happens to Your Blood During Pregnancy
During pregnancy, a woman’s body changes a lot, including blood volume. These changes help the growing fetus and get the mother ready for blood loss during delivery.
Normal Blood Volume Changes
The body’s blood volume goes up a lot during pregnancy. This is needed for the growing fetus and to get ready for childbirth.
The increase in blood volume is a critical adaptation that supports the pregnancy. It helps deliver oxygen and nutrients to the fetus and takes away waste. It also helps the mother’s body handle blood loss during delivery.
The 1-1.5 Liter Increase in Blood Volume
A pregnant woman’s blood volume usually goes up by 1 to 1.5 liters. This is a big jump, up to 50% more blood.
| Parameter | Non-Pregnant | Pregnant |
| Blood Volume (liters) | 4-4.5 | 5-6 |
| Red Blood Cell Mass | Normal | Increased by 20-30% |
| Plasma Volume | Normal | Increased by 30-50% |
The table shows plasma volume goes up more than red blood cells. This leads to hemodilution or “dilutional anemia.” It’s a normal part of pregnancy.
“The increase in blood volume during pregnancy is a vital adaptation that supports the health of both the mother and the fetus.”
Knowing about these changes helps take care of pregnant women. It also helps spot any blood volume or anemia problems.
Physiological Anemia: A Normal Adaptation in Pregnancy
Physiological anemia in pregnancy is common. It happens when red blood cells get diluted because of more blood plasma. This is a normal change the body makes to get ready for pregnancy.
Definition and Mechanism
Physiological anemia, or dilutional anemia, happens when plasma volume grows faster than red blood cell mass. Pregnancy makes the body produce more blood plasma. This is to help the growing fetus and prepare for blood loss during delivery.
This change is key for the health of both mom and baby. The extra plasma ensures enough blood flow to the placenta. It helps with the exchange of nutrients and waste between mom and baby.
Why It’s Called “Dilutional Anemia”
The term “dilutional anemia” comes from the dilution of red blood cells in more plasma. It’s not because of fewer red blood cells or more destruction. It’s a relative anemia, where the total number of red blood cells might go up, but not as much as plasma.
Knowing that physiological anemia is normal in pregnancy can ease worries about low hemoglobin or hematocrit levels. But, it’s vital to tell it apart from pathological anemia. The latter can have serious effects on both mom and baby’s health.
Key Fact #1: Blood Plasma Increases More Than Red Blood Cells
Pregnancy brings a unique change: blood plasma grows more than red blood cells. This is key for the growing fetus and getting ready for blood loss during delivery.
The 30-50% Increase in Total Blood Volume
Pregnancy boosts total blood volume by 30% to 50%. This big jump helps meet the needs of the mother and fetus. It also prepares for blood loss during childbirth. Plasma grows more than red blood cells.
Disproportionate Rise in Plasma vs. Red Blood Cells
Plasma volume grows more than red blood cells, causing hemodilution. While red blood cells increase by 20-30%, plasma can go up by 50%. This disproportionate increase leads to physiological anemia in pregnancy.
Healthcare providers need to understand this to spot normal changes versus serious issues that need treatment.
Key Fact #2: Normal Hemoglobin and Hematocrit Changes
Hemoglobin and hematocrit levels change a lot during pregnancy. This is because the body is getting ready to support the growing baby. These changes happen because of the body’s natural adjustments during pregnancy.
Pre-Pregnancy vs. Pregnancy Values
Before a woman gets pregnant, her hemoglobin and hematocrit levels are usually in certain ranges. Hemoglobin is around 12-16 g/dl, and hematocrit is between 38-45%. But, during pregnancy, these numbers change because of the increase in blood volume.
The blood volume grows more than the number of red blood cells. This leads to lower hemoglobin and hematocrit levels. This change is normal and usually not a worry.
The Drop from 38-45% to 34% Hematocrit
Hematocrit levels, which show the amount of red blood cells in the blood, go down during pregnancy. On average, they drop from 38-45% before pregnancy to about 34% during it.
Key changes include:
- A decrease in hematocrit levels to accommodate the increased blood volume
- A dilutional effect on hemoglobin levels due to increased plasma volume
- Adaptation to support the increased metabolic demands of pregnancy
It’s important for doctors to know about these changes. This helps them tell the difference between normal changes and health problems.
By watching these changes, doctors can spot any problems early. This means they can act fast if needed.
Key Fact #3: The Purpose of Hemodilution in Pregnancy
Hemodilution is a key adaptation that supports the health of both the mother and the developing fetus. It is vital for ensuring that the placenta gets enough blood. This is necessary for the fetus’s growth and development.
Supporting Placental Circulation
The increase in blood volume, mainly plasma, helps support the placental circulation. This is key for delivering oxygen and nutrients to the fetus. The placenta needs a lot of blood to work well, and hemodilution makes sure it gets it.
- Enhances oxygen delivery to the fetus
- Supports the removal of waste products from the fetus
- Facilitates the exchange of nutrients and gases between mother and fetus
Benefits for Maternal Cardiovascular System
Hemodilution also benefits the maternal cardiovascular system. It increases blood volume, preparing the mother’s body for blood loss during delivery. This adaptation lowers the risk of heart problems during childbirth.
- Reduced risk of thromboembolic events due to decreased blood viscosity
- Improved cardiac output to meet the increased demands of pregnancy
- Enhanced ability to compensate for blood loss during delivery
In conclusion, hemodilution is vital for supporting both the placental circulation and the maternal cardiovascular system. It shows its importance in a healthy pregnancy.
Key Fact #4: Distinguishing Physiological from Pathological Anemia
It’s important to know the difference between physiological and pathological anemia during pregnancy. Physiological anemia is normal and happens because of pregnancy. But, pathological anemia means there’s a health problem that needs doctor’s care.
Clinical Definitions and Thresholds
Physiological anemia, or dilutional anemia, happens when plasma volume grows more than red blood cells. The World Health Organization says anemia in pregnancy is when hemoglobin is under 11 g/dl. But, this number can change based on how far along you are and other things.
Knowing the clinical definition of anemia is key. It helps tell if it’s physiological or pathological. Hemoglobin levels are a main clue, with under 11 g/dl being anemic. But, other things like pregnancy stage and individual differences also matter.
When Hemoglobin Below 11 g/dl Indicates a Problem
A hemoglobin level under 11 g/dl doesn’t always mean you have pathological anemia. But, if you have other symptoms or very low hemoglobin (like under 10 g/dl), it could be a sign of a problem. Iron deficiency is a common cause of pathological anemia in pregnancy.
| Hemoglobin Level (g/dl) | Interpretation |
| Above 11 | Normal |
| 10-10.9 | Mild Anemia |
| Below 10 | Significant Anemia, potentially pathological |
Healthcare providers must look at the whole picture. They consider symptoms, lab results, and medical history to figure out if anemia is physiological or pathological.
Key Fact #5: Common Symptoms and Their Interpretation
During pregnancy, common anemia symptoms include fatigue, weakness, and shortness of breath. These can really affect your daily life. It’s important to understand these symptoms and know when to see a doctor for a healthy pregnancy.
Fatigue, Paleness, and Shortness of Breath
Fatigue is a big issue for pregnant women, often because of iron and nutrient needs. Paleness or pallor is another sign of anemia, though it might not be easy to spot in everyone. Shortness of breath happens when blood can’t carry enough oxygen.
- Fatigue and weakness due to reduced red blood cell mass
- Paleness or pallor as a visible sign of anemia
- Shortness of breath resulting from decreased oxygen delivery
These symptoms can be worrying, but it’s key to tell normal pregnancy discomforts from serious signs. For more on anemia in pregnancy, check out studies on PubMed Central.
When Symptoms Warrant Medical Attention
While some fatigue and shortness of breath are normal in pregnancy, other times they mean something serious. You should see a doctor if you have:
- Severe or persistent fatigue that makes daily tasks hard
- Dizziness or fainting spells
- Rapid or irregular heartbeat
Doctors can check how bad anemia is with blood tests and give the right treatment. As studies show, “Anemia in pregnancy is linked to higher risks of preterm delivery, low birth weight, and health problems for both mom and baby” (
A strong link between maternal anemia and bad pregnancy outcomes has been found.
In summary, while some anemia symptoms are normal in pregnancy, knowing when they’re serious is key. Regular prenatal visits and talking openly with your healthcare team are vital for a healthy pregnancy.
Key Fact #6: Iron Deficiency vs. Physiological Anemia
Pregnancy changes the body in many ways, including blood composition. This can lead to different anemia types. Iron deficiency anemia and physiological anemia are two conditions often talked about during pregnancy.
The Most Common Cause of True Anemia in Pregnancy
Iron deficiency is the main cause of true anemia in pregnant women. It’s different from physiological anemia, which is a normal pregnancy change. Iron deficiency anemia means there’s a health issue that needs doctor’s care.
The body needs more iron during pregnancy. This is because of the increase in blood volume and the needs of the growing fetus.
Iron deficiency anemia happens when the body can’t make enough hemoglobin. Hemoglobin is a protein in red blood cells that carries oxygen. Without enough iron, the body can’t make enough hemoglobin. This leads to fatigue, weakness, and other problems for both the mother and the baby.
Laboratory Markers to Differentiate the Two
To tell iron deficiency anemia from physiological anemia, doctors use lab tests. They look at hemoglobin levels, hematocrit, mean corpuscular volume (MCV), and serum ferritin levels.
| Laboratory Marker | Physiological Anemia | Iron Deficiency Anemia |
| Hemoglobin | Typically within normal limits or slightly decreased | Decreased below normal limits |
| MCV | Normal or slightly decreased | Decreased (microcytic anemia) |
| Serum Ferritin | Normal or elevated | Decreased |
By looking at these lab markers, doctors can tell if a pregnant woman has physiological anemia or iron deficiency anemia. This helps them give the right care and treatment.
Key Fact #7: Management Approaches for Blood Changes
Managing blood changes is key for a healthy pregnancy. The body’s blood volume and makeup change a lot during pregnancy. These changes can affect the health of both the mother and the baby.
Dietary Recommendations and Monitoring
Eating a balanced diet is very important during pregnancy. Foods rich in iron, folate, and vitamin B12 help make red blood cells. These nutrients are essential for the mother and the baby.
It’s also important to keep an eye on blood levels. Doctors often do blood tests to check for anemia or other blood problems.
When Supplementation Is Necessary
Sometimes, just eating right isn’t enough. That’s when supplements come in. Iron supplements, for example, are often given to pregnant women to prevent anemia.
It’s important for pregnant women to follow their doctor’s advice on supplements. They should also talk about any side effects or worries they have.
Managing blood changes in pregnancy involves diet, monitoring, and supplements when needed. Working with a healthcare provider helps ensure a healthy pregnancy.
Special Considerations for High-Risk Pregnancies
Managing high-risk pregnancies means knowing how multiple babies and health issues affect blood volume. Women with these conditions need extra care to keep them and their babies safe.
Multiple Gestations and Blood Volume Changes
Pregnancies with twins or more see bigger changes in blood volume than single babies. This can cause hemodilution, where plasma volume grows faster than red blood cells. This might lower hematocrit levels more.
Women expecting twins or more might see their blood volume increase by up to 60%. This is more than the 40-50% increase seen in single pregnancies. This extra demand can stress the heart and may require more blood checks.
Pre-existing Conditions and Their Impact
Pre-existing health issues can make pregnancy harder by affecting blood volume changes. Problems like heart disease or chronic anemia can make pregnancy more challenging. They might lead to worse anemia or other issues.
For example, a woman with heart disease needs careful management to handle pregnancy’s blood volume increase. Women with chronic anemia might need iron or other treatments to manage their condition during pregnancy.
Healthcare providers must understand these challenges in high-risk pregnancies. Knowing the unique issues of multiple babies and health conditions helps them give better care.
Conclusion: Embracing the Normal Adaptations of Pregnancy
It’s key to understand and accept the normal changes in pregnancy for a healthy journey. Physiological anemia, where red blood cells get diluted, is a common change. It happens because the body needs to support the growing baby and get ready for delivery.
This type of anemia is caused by the body making more blood plasma than red blood cells. This imbalance lowers the hematocrit levels. It’s important to know this is normal and not harmful.
Knowing the difference between normal and harmful anemia is vital. The right knowledge helps expectant mothers make better choices for their health and their baby’s.
By accepting these changes, mothers can have a healthier pregnancy. This leads to a more positive experience for everyone involved.
FAQ
What is physiological anemia in pregnancy?
Physiological anemia in pregnancy is when the body’s blood volume increases. This dilutes the red blood cells, lowering hemoglobin levels.
Is physiological anemia in pregnancy a cause for concern?
Usually, physiological anemia is not a worry. But, it’s key to tell it apart from pathological anemia, which might signal a health issue.
How does pregnancy affect blood volume?
Pregnancy boosts blood volume by 30-50%. Plasma volume grows more than red blood cells, causing hemodilution.
What are the normal hemoglobin and hematocrit changes during pregnancy?
Pregnancy lowers hemoglobin and hematocrit levels. Hematocrit might drop from 38-45% to about 34%.
What is the purpose of hemodilution in pregnancy?
Hemodilution aids the placenta and prepares the mother’s heart for delivery. It’s a natural adaptation.
How can I distinguish between physiological anemia and pathological anemia?
Use clinical guidelines and lab tests to tell them apart. Hemoglobin levels below 11 g/dl are a clue.
What are the common symptoms of anemia during pregnancy?
Symptoms include tiredness, paleness, and shortness of breath. Seek help if these signs are severe or last long.
How is iron deficiency anemia different from physiological anemia?
Iron deficiency anemia lacks iron, while physiological anemia is a pregnancy adaptation. Lab tests can tell them apart.
How are blood changes during pregnancy managed?
Management includes diet advice, monitoring, and supplements when needed.
Are there any special considerations for high-risk pregnancies?
Yes, high-risk pregnancies need extra care. They affect blood volume and anemia differently.
How many liters of blood are in the human body during pregnancy?
Blood volume increases by 1-1.5 liters in pregnancy. It ranges from 5-6 liters, depending on size and other factors.
References
- Berkey, F. J. (2010). Managing the adverse effects of radiation therapy. American Family Physician, 82(4), 381–388.
https://pubmed.ncbi.nlm.nih.gov/20704169
- American Cancer Society. (2025). Radiation Therapy Side Effects. Cancer.org.
