Fetal anemia is a condition where a developing baby lacks sufficient healthy red blood cells in the womb. Red blood cells carry oxygen via hemoglobin. Too few red blood cells mean the fetus receives insufficient oxygen, affecting its growth and development.
This condition ranges from mild to severe. Severe cases strain the fetal heart, as it works harder to pump blood. Untreated, this can lead to heart failure and hydrops fetalis, a fluid buildup.
Common Causes
A frequent cause of fetal anemia is red blood cell alloimmunization, where the mother’s immune system produces antibodies against the baby’s red blood cells. This often happens with incompatible blood types, like Rh incompatibility (Rh-negative mother, Rh-positive baby). Maternal antibodies cross the placenta, destroying fetal red blood cells. Kell disease is another alloimmunization form leading to severe fetal anemia.
Infections passed from mother to baby during pregnancy can also induce fetal anemia. Parvovirus B19 (fifth disease) can temporarily stop fetal red blood cell production.
Twin-to-twin transfusion syndrome (TTTS) can cause fetal anemia in identical twins sharing a placenta. Uneven blood flow through shared vessels leads to one twin becoming anemic from too little blood, while the other receives too much. Inherited conditions, like alpha thalassemia, can also impair the fetus’s ability to produce healthy red blood cells.
How Fetal Anemia is Diagnosed
Fetal anemia diagnosis often begins with non-invasive specialized ultrasound examinations. A primary indicator is increased blood flow velocity in the fetal brain’s middle cerebral artery (MCA-PSV). This suggests the baby’s body works harder to deliver oxygen due to fewer red blood cells.
Ultrasound can also reveal other signs of severe anemia, such as hydrops fetalis—an abnormal fluid accumulation in at least two areas (e.g., heart, lungs, abdomen). These fluid collections indicate the heart struggles to pump blood effectively, a consequence of prolonged oxygen deprivation. Early detection allows timely intervention.
If non-invasive tests suggest fetal anemia, definitive diagnostic procedures may follow. Cordocentesis (fetal blood sampling) involves inserting a thin needle into the umbilical cord to obtain a fetal blood sample. This precisely measures hemoglobin levels and confirms anemia severity. Amniocentesis might also assess for infections or genetic conditions causing the anemia.
Management and Treatment
The primary treatment for significant fetal anemia is intrauterine blood transfusion, performed while the baby is in the womb. This involves carefully transfusing donor red blood cells directly into the baby’s umbilical vein or fetal abdominal cavity, using ultrasound guidance. The goal is to increase the baby’s red blood cell count and improve oxygen delivery.
These transfusions prevent severe complications like heart failure and hydrops fetalis, allowing the fetus to develop until mature enough for birth. Multiple transfusions may be necessary, depending on anemia severity and the baby’s response. Timing and frequency are carefully determined by ongoing fetal monitoring.
If anemia is severe and close to term, early delivery might be considered. This decision is made when continuing the pregnancy poses greater risks than premature birth. The overall aim of any intervention is to support the baby’s health and development, mitigating insufficient red blood cell effects.
Outlook and Potential Outcomes
The outlook for fetuses diagnosed with anemia has improved due to advancements in prenatal diagnosis and treatment. Prognosis depends on the underlying cause, severity at diagnosis, and treatment effectiveness. With timely interventions like intrauterine blood transfusions, many fetuses achieve positive outcomes.
While most cases respond well to treatment, complications can arise. These include short-term risks from the transfusion procedure, such as infection or premature labor. Long-term outcomes are influenced by hydrops fetalis development and persistence, as severe, prolonged hydrops can lead to developmental challenges.
Most fetuses treated for anemia experience excellent outcomes, especially with early detection and effective management. Ongoing monitoring after birth is often recommended to ensure the baby thrives and to address any residual effects or underlying causes.