Hydrops fetalisHydrops fetalis A serious, sometimes fatal condition in which fluid builds up in a baby’s tissues and organs due to severe anemia from HDFN. is a complication of severe anemiaAnemia A condition that occurs when the body doesn’t have enough healthy red blood cells to carry oxygen to its tissues. In HDFN, anemia occurs when maternal antibodies destroy fetal red blood cells., which is most often caused by alloimmunizationAlloimmunization When a person’s immune system develops antibodies against foreign antigens from the same species—such as when an Rh-negative mother’s body forms antibodies against her baby’s Rh-positive red blood cells. or hemolytic disease of the fetus and newborn (HDFN). Hydrops fetalis is rare, but it can have life-threatening consequences if not treated urgently.
TSevere hydrops fetalis can put strain on the heart, which can cause accumulation of fluid in the tissue and organs, as well as swelling around the heart, lungs and abdomen. Around 50% of unborn babies with hydrops fetalis don’t survive, so urgent treatment and sometimes a preterm delivery are required to ensure the best outcomes for the baby.
What is HDFN?
Hemolytic disease of the fetus and newborn (HDFN) is an immune-mediated red blood cell disorder that occurs when a baby’s RBCs break down quickly, which is called hemolysis. HDFN is caused by a mismatch between a mother’s and her baby’s blood type (A, B, AB, or O) or Rhesus (RhRh factor A protein or antigen found on red blood cells. When an Rh-negative mother carries an Rh-positive fetus, her immune system may make antibodies that attack the fetus' red blood cells.) factor (Rh-positiveRh-Positive A blood type trait that means your red blood cells have the Rh(D) antigen. or Rh-negativeRh-Negative A blood type trait that means your red blood cells lack the Rh(D) antigen.) during pregnancy.
How does hydrops fetalis occur?
In HDFN, maternal antibodiesAntibody A protein made by the immune system that recognizes and attacks foreign substances, such as bacteria, or in HDFN, fetal red blood cells carrying incompatible antigens. cross the placenta to attack the fetus’s red blood cells. As the red blood cells break down, anemia develops. If this leads to severe anemia, strain is put on the fetus’s heart as it struggles to pump oxygen-rich blood around the body and less oxygen is delivered to the body’s tissues and organs, causing damage and leading to heart failure.
During heart failure, fluid accumulates around the heart, lungs and abdomen. It also gathers in the skin, causing edema or swelling.
What are the risks of hydrops fetalis?
When severe anemia is detected, urgent treatment is required to avoid serious complications such as hydrops fetalis. Without effective treatment or early delivery to allow for urgent medical intervention, hydrops fetalis can, in some cases, lead to cardiac arrest, fetal death or a miscarriage during pregnancy.
Following delivery, a newborn affected by hydrops fetalis can experience respiratory distress, feeding difficulties, brain damage, developmental delays and cerebral palsy. Urgent intervention after birth is necessary to ease breathing difficulties with a ventilator or extra oxygen and to remove extra fluid around the heart and lungs with a needle.
Read more about HDFN causes and risk factors
Diagnosing hydrops fetalis in pregnancy
Fetal anemia is detected via MCA Doppler, which measures blood flow velocity in the fetal brain’s middle cerebral artery. Hydrops fetalis is detected via ultrasoundUltrasound An imaging test that uses sound waves to monitor fetal growth, development and signs of complications during pregnancy. when swelling is identified.
Treating hydrops fetalis in HDFN
Early diagnosis of anemia and proactive treatment with intrauterine transfusions and intravenous immunoglobulinIntravenous immunoglobulin A therapy made from donated antibodies that may help reduce the mother’s immune response and protect the fetus. during pregnancy can delay or prevent the onset of severe anemia and the complication of hydrops fetalis.
Early delivery may be required to remove the baby from the effects of the maternal antibodies and to allow for urgent treatment to resolve hydrops fetalis.
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