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Environmental Public Health Tracking: Hypoplastic Left Heart Syndrome Data

A birth defect is a problem that happens while the baby is developing in the mother's body. Most birth defects happen during the first three months of pregnancy. A birth defect may affect how the body looks, works, or both.

Access birth defects data

Hypoplastic left heart syndrome (HLHS) is one type of birth defect. Review the FAQs below for more information about hypoplastic left heart syndrome.

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Hypoplastic (pronounced hi-puh-plas-tik) left heart syndrome (HLHS) is an underdeveloped left side of the heart that is present at birth. The underdevelopment causes a decrease in blood flow through the body. Babies with HLHS might look normal at birth but will develop symptoms within a few days.

Researchers estimate about 1,025 babies in the United States are born with HLHS each year. In other words, about 1 out of every 3,841 babies born will be born with HLHS each year.*

**Mai CT, Isenburg JL, Canfield MA, Meyer RE, Correa A, Alverson CJ, Lupo PJ, Riehle‐Colarusso T, Cho SJ, Aggarwal D, Kirby RS. "National population‐based estimates for major birth defects, 2010–2014." Birth Defects Research. 2019; 111(18): 1420-1435.

Although a baby with HLHS may look normal at birth, several symptoms may appear shortly after:

  • Poor feeding
  • Problems breathing
  • Pounding heart
  • Weak pulse
  • Ashen or bluish skin color

Learn more about symptoms on the CDC's (Centers for Disease Control and Prevention) Facts about Hypoplastic Left Heart Syndrome page.

There is no known cause for hypoplastic left heart syndrome (HLHS). CDC works with many other researchers to study risk factors that can increase the chance of having a baby with HLHS, as well as outcomes of babies with the defect. Learn more about causes and risk factors on the CDC's Facts about Hypoplastic Left Heart Syndrome page.

HLHS cannot be prevented. However, mothers can take steps before and during pregnancy to have a healthy pregnancy. Steps include taking a daily multivitamin with folic acid (400 micrograms), not smoking, and not drinking alcohol during pregnancy.

Last revised May 8, 2023