Understanding Congenital Hypoplastic Left Heart Syndrome
• What is Hypoplastic Left heart Syndrome?
• How common is HLHS and what causes it?
• How is HLHS detected during prenancy?
• How will my preganancy be manged now that HLHS has been detected?
• How will HLHS be treated after birth?
• What is the long-term outlook for babies with HLHS?
• What are the chances I could have another baby with HLHS?
• What can I expect from the specialists at Morgan Stanley
WHAT IS HYPOPLASTIC LEFT HEART SYNDROME?
Hypoplastic left heart syndrome (HLHS) is a condition
in which the structures of the left side of the heart are
underdeveloped and unable to function properly at birth.
Specifically, the left ventricle, the aorta, the aortic and
mitral valves, and the aortic arch are too small to be able
to support circulation to the body, with varying degrees
In the normal heart, unoxygenated blood returns from the
body to the right atrium and then the right ventricle, where
it is pumped through the pulmonary artery to the lungs.
After the blood is oxygenated in the lungs, it returns
to the left atrium of the heart and is passed to the left
ventricle. From the left ventricle it is pumped out to the
body through the aorta. In HLHS the left ventricle is too
small and weak to provide the necessary blood to the
is fatal if left untreated.
HOW COMMON IS HLHS AND WHAT CAUSES IT?
HLHS is one of the most common serious heart defects in newborn
babies, seen in 1-4 out of every 10,000 live births. It is believed to
make up 9% of all cases of heart defects present at birth, and is twice
as common in boys as girls.
No one knows for sure what causes HLHS, but it likely happens very
early in pregnancy when the heart is developing, around 5-8 weeks of
HOW IS HLHS DETECTED DURING PREGNANCY?
HLHS is usually detected during pregnancy through the ultrasound
(sonogram) performed to check fetal development in the second
trimester. In looking at the four chambers of the fetal heart, the left
ventricle appears much smaller than the right ventricle, and the other
structures of the left side of the heart will appear different as well.
The diagnosis of HLHS is usually made following a fetal echocardiogram,
which is an ultrasound of the developing heart. At NewYork-Presbyterian
Morgan Stanley Children's Hospital/Columbia University Medical Center, all fetal echocardiograms for HLHS are performed by Pediatric
Cardiologists with expertise in the technique. Unfortunately, some
cases of HLHS evolve over the course of the pregnancy and can not
be detected until late in the third trimester. Of the cases diagnosed
prenatally, almost all are confirmed after birth.
HOW WILL MY PREGNANCY BE MANAGED NOW THAT HLHS HAS BEEN DETECTED?
An ultrasound will carefully examine the fetal development and exclude
any other birth defects that are more frequently seen with HLHS, such
as other types of heart defects, abnormalities in the digestive system,
and brain malformations. Prenatal care should be managed by a
Maternal-Fetal Medicine specialist (MFM), an obstetrician with special
training and expertise in high-risk pregnancy. A fetal echocardiogram will
be performed by a Pediatric Cardiologist to confirm the diagnosis and exclude
other heart problems. Furthermore, a procedure called amniocentesis
may be offered to you to examine the baby's chromosomes, since
HLHS babies are more likely to have a chromosomal abnormality.
As your delivery date approaches, induction of labor or a cesarean section
may be planned to optimize the delivery and ensure that the necessary
specialists are available to care for the baby immediately after birth.
However, labor management does not need to be changed because
your baby has HLHS.
HOW WILL THE HLHS BE TREATED AFTER BIRTH?
Until recently, HLHS was considered so serious that hope for survival
was grim, and most HLHS babies were given comfort care and allowed
to pass away on their own a few days after birth. HLHS remains a serious
condition, but the surgical options have improved the outlook for these
babies, and more parents are opting for surgery. In some cases, where
the condition is so severe it can not be improved with surgery, heart
transplantation may be the only option for survival.
The three surgeries needed to treat HLHS are complex but basically
involve making the right side of the heart do the work of the left side as
well. The details and timing of each stage are individualized for each
case, so be sure to discuss them in detail with your medical team. If you
decide that you would like your baby to have surgery, you might expect
The first stage is called the Norwood operation, and takes place
soon after birth. The heart is reconstructed to allow the right ventricle
to pump blood to the body (instead of the left ventricle, which is too
small), and something called a BT Shunt is performed which allows
the right ventricle to maintain blood flow to the lungs.
- At around three to eight months of age, the lungs will be mature
enough for the second surgery, known as the bi-directional Glenn.
This surgery reduces the workload of the right ventricle so it only
pumps blood to the body (instead of both the body and lungs) and
allows most of the blood from the body to flow directly into the lungs.
- Between ages two and five, the final surgery is performed, known as the
Fontan operation. This surgery allows all of the blood from the body
to flow directly to the lungs by creating a channel through the heart
to direct it. The result is a complete separation of the unoxygenated
blood (from the body) and the oxygenated blood (from the lungs),
such that all the blood from the body flows into the lungs directly, and
the right ventricle pumps the blood from the lungs to the body.
WHAT IS THE LONG-TERM OUTLOOK FOR BABIES WITH HLHS?
Long-term outcome for babies with HLHS has improved over the years
as surgery has become better and heart transplantation improved.
At NewYork-Presbyterian Morgan Stanley Children's Hospital/Columbia
University Medical Center, we have the most experienced surgical team
in the tri-state area, and almost all cases of HLHS detected at birth at
other hospitals come to us.
Because surgery for HLHS is so new, the long-term effects of the
condition or multiple surgeries are unknown. More studies are needed
to determine the impact of HLHS and its treatment on the intellectual
development of affected children and on the quality of life they can expect.
WHAT ARE THE CHANCES I COULD HAVE ANOTHER BABY WITH HLHS?
In most cases, HLHS occurs due to chance alone, so the chances for
a second affected pregnancy are generally only 2-3%, though some
studies suggest a higher chance of up to 13.5%. Speak with your
Genetic Counselor and Geneticist to determine your specific chances
for another affected pregnancy.
WHAT CAN I EXPECT FROM THE SPECIALISTS AT MORGAN STANLEY CHILDREN'S HOSPITAL?
The specialists at Morgan Stanley Children's Hospital are among the
most experienced with HLHS in the United States. The Center approach
includes a whole team in your prenatal care to optimize the chances for
your baby's well-being after birth. You might expect to meet the following
- Maternal-Fetal Medicine (MFM)—you will see one of a team of MFMs
throughout your pregnancy, and every effort will be made for that
doctor to deliver your baby.
- Pediatric Cardiology—Pediatric cardiology performs fetal echocardiograms
in the prenatal setting to diagnose HLHS; all cases are
confirmed after birth.
- Pediatric Cardiothoracic Surgery (CT Surgery)—A recently released
report by the New York State Department of Health has shown that
NewYork-Presbyterian Morgan Stanley Children's Hospital/Columbia
University Medical Center and the NewYork-Presbyterian Komansky
Center for Children's Health/Weill Cornell Medical Center are leaders in
the state for best outcomes for surgeries performed on children with
congenital heart defects.
- Genetics—While you may have already met with Genetics during
pregnancy, you will likely speak with them again after the baby is born.
- Neonatology—since the Center's inception, our top-ranked 50-
bed NICU regularly cares for babies with HLHS. Our staff has been
continuously recognized for their excellence.
You should discuss with your Care Coordinator how these specialists
will be involved in your care during pregnancy. The well-being of you and
your baby are extremely important to everyone involved in your care.
Together we are all dedicated to giving you the best pregnancy and
healthiest outlook for your child.