Hydrops Fetalis: What Is It?

Medically Reviewed by Dan Brennan, MD on September 05, 2023
3 min read

Hydrops fetalis is a life-threatening condition where excessive amounts of fluid build up inside an unborn or newborn baby’s body. Fluid build up can occur in any part of the body, but it is most commonly seen in the abdominal area, near the heart and lungs, and under the skin. When left untreated, the excess fluid produced by hydrops fetalis can place stress on the baby's heart and other vital organs, putting them seriously at risk.

Each baby’s symptoms can vary, but these are the most common.

Hydrops fetalis during pregnancy:

● Larger than average amount of amniotic fluid

● Thick placenta

● Enlarged spleen and heart

● Fluid buildup around the baby’s organs, heart or lungs

Hydrops fetalis after pregnancy:

● Pale skin

● Severe sweating

● Trouble breathing

● Enlarged liver and spleen

There are 2 types of hydrops fetalis:

Non-immune hydrops. This is the more common type of hydrops, occurring in about 80-90% of cases. It’s caused by a genetic disorder or congenital disability that interferes with the baby's ability to manage fluid.

Immune hydrops. This rarer type occurs when there is an incompatibility between the red blood cells of the mother and baby. For instance, when a pregnant woman has Rh-negative blood, and her unborn baby has Rh-positive blood. The mother's immune system treats the baby's Rh-positive red blood cells as "foreign invaders" and sends out antibodies to fight them. 

This leads to the destruction of many of the baby's red blood cells, causing a medical condition called anemia. If your baby becomes anemic, it means that it lacks enough healthy red blood cells to carry adequate oxygen through its body. In some cases, anemia creates only mild to moderate health problems for the baby. In other cases, anemia can lead to life-threatening heart failure.

Hydrops fetalis is not a disease in itself. Instead, it’s caused by a different medical condition. There are a few different medical conditions and complications that may cause hydrops fetalis.

Hemolytic disease of the newborn. Also known as erythroblastosis fetalis, this is a blood disorder that occurs when the blood types of a mother and baby are incompatible.

Severe anemia. Anemia is a common blood disorder that occurs when the body has fewer red blood cells than normal. Red blood cells carry oxygen throughout the body, if there aren’t enough of these cells or this protein, it results in anemia.

Infection. If there is an infection present at birth, it may cause hydrops fetalis.

Heart and lung defects. If the baby’s heart or lung didn’t develop properly, it can be a contributing factor that causes hydrops fetalis.

Birth defects and congenital anomalies. About 3 to 4 percent of babies are born with some type of birth defect. A birth defect is a health problem or a physical abnormality. It can be very mild or severe. If your baby has a birth defect, it increases the likelihood that they will develop hydrops fetalis.

Liver disease. If your child has liver problems, it often shows up as jaundice (yellowing of skin and eyes) swelling in the abdomen, fever and pain. Liver disease can be a medical condition which leads to hydrops fetalis.

Your doctor will often diagnose hydrops fetalis during a routine prenatal ultrasound exam. If abnormal amounts of fluid are found in two or more areas of your baby's body, it may indicate hydrops fetalis. The doctor will also check for other symptoms such as a large amount of amniotic fluid, a thickened placenta, enlarged heart, liver, or spleen.

Hydrops fetalis can also be diagnosed through blood tests which can reveal red blood cell incompatibility between mother and baby.

If diagnosed during pregnancy, hydrops fetalis is not always treatable and may involve early labor. 

If a baby is born with hydrops fetalis, your baby will need specialized medical care. They may need a breathing machine (ventilator), and your doctor may need to use a needle to remove excess fluid from the spaces around the baby's heart, lungs, and abdomen.

Your baby will need to stay at the hospital under careful observation by your medical team until the underlying disease-causing hydrops fetalis has been stabilized.