What is fetal anemia?

Fetal anemia is a condition where a baby has a low number of red blood cells before birth.  

Red blood cells carry oxygen through the body. When the red blood cell count is low, the baby may not get enough oxygen to grow and develop normally. 

Fetal anemia can range from mild to severe. With early diagnosis and expert care, many babies can be treated safely during pregnancy.

What happens if a fetus has anemia?

When a fetus has anemia, the heart must work harder to move oxygen through the body. Over time, severe anemia can lead to: 

• Swelling in the fetus (called hydrops) 
• Heart strain or heart failure 
• Early delivery 
• Fetal death 

Close monitoring and timely treatment can prevent these complications in many cases.

What are the causes of fetal anemia?

Fetal anemia has several possible causes. The most common include: 

Rh alloimmunization
This is the most common cause. It happens when the pregnant person’s immune system makes antibodies that attack the baby’s red blood cells. These antibodies break down the baby’s blood cells and lead to anemia. 

Infections 
Certain viruses, such as parvovirus or cytomegalovirus (CMV), can affect how a fetus makes red blood cells and platelets or cause the body to destroy them.

Genetic or inherited blood conditions 
Some babies have inherited conditions that affect the shape or function of red blood cells. These conditions can lead to anemia before birth. 

Our team carefully evaluates the cause of fetal anemia because treatment and follow-up depend on the underlying reason.

What are the signs and symptoms of fetal anemia?

Most pregnant people do not feel symptoms of fetal anemia. Doctors usually identify if a fetus is at risk for fetal anemia during routine prenatal care or ultrasound. 

Signs of fetal anemia may include: 

• Increased blood flow speed in certain blood vessels 
• Changes seen on ultrasound 
• Swelling in the fetus 

If you are at risk for fetal anemia due to maternal antibodies or recent viral exposure, your care team will monitor you closely with blood tests and ultrasound.  

How is fetal anemia diagnosed?

Screening with ultrasound

Ultrasound is the main screening tool for fetal anemia. This specialized test is typically performed by a maternal-fetal medicine (MFM) specialist — a doctor with advanced training in high-risk pregnancies.

During the exam, the doctor measures blood flow in a vessel in the baby’s brain called the middle cerebral artery. When a fetus has anemia, blood moves faster through this vessel. If the speed is higher than expected for gestational age, the baby may be at risk. 

Because these measurements must be precise, experience in fetal imaging is important. At the Center for Fetal Diagnosis and Treatment, our team performs and interprets these studies every day, helping ensure accurate diagnosis and timely care.

Confirming the diagnosis

If testing suggests fetal anemia, doctors may confirm it by taking a small blood sample from the umbilical cord. Using ultrasound for guidance, a specialist carefully places a thin needle into the umbilical cord to collect blood. This procedure allows the team to measure the baby’s blood count and determine the severity of anemia. 

At Children’s Hospital of Philadelphia (CHOP), this testing is performed by highly experienced fetal therapy specialists who focus on safety for both parent and baby.

How is fetal anemia treated?

Treatment depends on how severe the anemia is and what is causing it. 

Intrauterine blood transfusion 

If fetal anemia is confirmed, doctors can treat it before birth with a blood transfusion.

Using ultrasound guidance, a specialist places a thin needle into the umbilical cord. If testing confirms anemia, the same needle entry is often used to give compatible donor blood directly to the fetus. This allows diagnosis and treatment in a single procedure whenever possible. The transfusion raises the baby’s red blood cell count and improves oxygen delivery. 

During the procedure: 

• The fetal heart rate is monitored continuously  
• Our team carefully tracks your baby’s response 
• You and your baby are observed after the procedure 

Some babies need more than one transfusion during pregnancy. Our team plans each step based on how quickly the baby’s blood count is expected to change.

Ongoing monitoring

After treatment, regular ultrasounds check for signs that anemia is returning. Timing for additional transfusions is individualized for each pregnancy. 

Because our program is one of the most experienced in the world, families come to us for complex fetal transfusions and advanced care not widely available elsewhere. 

What follow-up care is needed?

Follow-up depends on the cause of fetal anemia and how your baby responds to treatment. 

During pregnancy: 

• Regular ultrasounds monitor blood flow and overall health 
• Additional transfusions may be needed 
• Delivery planning focuses on safety for parent and baby 

Most families can plan to deliver at their home hospital at or near full term. When appropriate, our team works closely with your obstetrician to coordinate care. 

In more complex cases, delivery at our Garbose Family Special Delivery Unit may be recommended to ensure immediate access to specialized newborn care. 

Before and after delivery, our pediatric hematology team partners with your baby’s primary care pediatrician to ensure a smooth transition and close follow-up. 

After birth: 

• Your baby’s blood count will be checked regularly 
• Some babies need additional transfusions after delivery 
• Care continues with pediatric specialists as needed 

Our coordinated team supports families through pregnancy, delivery and the newborn period. 

What is the long-term outlook?

The outlook for babies with fetal anemia is often very good when diagnosed early and treated by experienced specialists. 

• Rh-related fetal anemia: Most babies have no long-term effects after treatment. 
• Infection-related anemia: Many babies recover fully once the infection resolves. 
• Genetic conditions: Some children may need ongoing care or occasional transfusions. Rarely, a bone marrow transplant may be recommended.

Our fetal and pediatric experts work together to create a personalized plan for every child.

Why choose CHOP for fetal anemia care?

Families from around the world come to CHOP’s Center for Fetal Diagnosis and Treatment for fetal therapy because of our depth of experience and outcomes. 

We offer:  

• One of the largest and most experienced fetal therapy programs in the world 
• Specialists who helped pioneer fetal transfusion and other lifesaving procedures 
• Comprehensive care in one place, from diagnosis through delivery and beyond 
• Family-centered support, education and counseling
• Ongoing research that advances treatment and improves outcomes 

Under the leadership of Dr. Jena Miller, our team continues to advance the field and provide leading-edge care for babies with fetal anemia. 

Frequently asked questions

Can a baby survive fetal anemia

Yes. Many babies with fetal anemia do very well, especially when diagnosed early and treated by an experienced fetal therapy team. 

Is fetal anemia dangerous? 

Severe anemia can be serious if not treated. With close monitoring and timely care, many complications can be prevented. 

What is the most common cause of fetal anemia?

Rh alloimmunization, when maternal antibodies attack the baby’s red blood cells, is the most common cause. 

How common is fetal anemia?

Fetal anemia is rare. Many providers may see only a few cases. Specialized centers like ours have the experience needed to diagnose and treat it safely.