What congenital heart defects occur in trisomy 18?

Congenital heart defects are very common in babies with trisomy 18. Research estimates that between 80% and 90% of infants with the condition have a heart difference ^[1][2]. The most frequent issues are “holes in the heart” like ventricular septal defects (VSDs) and atrial septal defects (ASDs), as well as a patent ductus arteriosus (PDA) ^[3]. However, heart anatomy varies widely. Some babies have complex structural differences or abnormalities in their heart valves ^[4][5].

When it comes to care, major medical organizations emphasize that treatment decisions must be made on a case-by-case basis ^[6]. Your baby’s specific heart anatomy, how well their heart functions, and your family’s unique goals—not just the diagnosis of trisomy 18—will guide their care ^[6].

Common Heart Defects in Trisomy 18

While every baby is unique, several specific heart differences are frequently seen:

• Septal defects: The most common finding is a ventricular septal defect (VSD), a hole between the heart’s lower pumping chambers ^[3]. Atrial septal defects (ASDs) (a hole between the upper chambers) and atrioventricular (AV) canal defects (a large hole in the center of the heart) are also reported, though often less common than VSDs ^[3][7]. These holes can cause extra blood to flow into the lungs, sometimes leading to heart failure or lung damage. Some small defects may close or remain clinically insignificant, while larger ones require treatment.
• Patent ductus arteriosus (PDA): The ductus arteriosus is a normal fetal blood vessel that usually closes shortly after birth. In over 50% of babies with trisomy 18, it remains open (patent), which can lead to extra blood flowing into the lungs ^[3].
• Valve abnormalities: It is common for babies with trisomy 18 to have differences in how their heart valves are formed. Some babies have abnormalities in more than one heart valve (sometimes called polyvalvular disease), which can affect how blood is directed through the heart ^[2].
• Complex or obstructive defects: Less commonly, babies may have complex structural differences. These can include coarctation of the aorta (a narrowing of the main blood vessel leaving the heart) or an interrupted aortic arch ^[4][5]. Others might have underdeveloped (hypoplastic) heart chambers or narrowing or blockage of the pathway from the heart to the lungs (pulmonary stenosis or pulmonary atresia) ^[4][5].

How the Heart is Assessed

Understanding your baby’s heart structure is the critical first step in building a care plan.

• Echocardiogram (Echo): This specialized ultrasound of the heart provides detailed pictures of your baby’s anatomy. The cardiologist uses it to locate septal defects, check how well the heart muscle is pumping, and assess the valves ^[8]. The echo also estimates blood pressure in the lungs to look for signs of pulmonary hypertension (high pressure in the blood vessels of the lungs), a known risk in trisomy 18 ^[8][9].
• Cardiac Catheterization: In some complex cases, doctors may recommend a cardiac catheterization. This procedure uses a thin tube inserted into a blood vessel to directly measure blood pressure and flow in the heart and lungs ^[8][10]. Because it involves sedation or anesthesia and carries risks (like bleeding or heart rhythm issues), it is only used when the information gathered is expected to change the treatment plan. It does not by itself guarantee that surgery will be safe.

Treatment and Management Options

Because heart anatomy in trisomy 18 varies so much, there is no single treatment pathway. Expert guidelines recommend shared decision-making involving parents, cardiologists, surgeons, and palliative care teams ^[6][11]. Importantly, treating the heart defect will not cure trisomy 18 or remove its other medical challenges.

• Observation and Supportive Care: Minor defects may simply be monitored. For moderate or severe defects causing heart failure symptoms, medical management might include diuretics (water pills) to help remove extra fluid from the lungs ^[12]. Home oxygen or feeding tubes are sometimes used, but they are highly individualized. Oxygen is prescribed for specific needs and must be monitored carefully, as giving oxygen can sometimes unintentionally increase blood flow to the lungs in babies with certain defects. Tube feeding can improve nutrition but also carries burdens, so it must align with your family’s goals ^[13].
• Catheter-Based Treatments: For certain complex anatomies, a catheter procedure can stabilize the baby. For example, if a baby has a blockage like pulmonary atresia and their blood flow depends on the PDA staying open, doctors might place a stent to intentionally keep the PDA open ^[14]. This is very different from an open PDA that is causing dangerous lung overcirculation, which doctors might instead decide to close or manage with medications.
• Surgical Options: Some babies undergo heart surgery, such as placing a band around the lung artery (pulmonary artery banding) to limit excessive blood flow ^[10][15]. This is an individualized, palliative procedure for carefully selected babies; while some may eventually go on to have a second surgery to patch a VSD months later, this later repair is not guaranteed or appropriate for everyone.
• Weighing the Risks of Surgery: Observational studies suggest that in carefully selected cases, heart surgery can extend survival and increase the likelihood of a baby being discharged home ^[16][17]. However, these studies are limited by selection bias (meaning babies chosen for surgery may have been healthier overall). Surgery carries substantial risks, and babies with severe other medical needs—especially those requiring a mechanical ventilator (breathing machine) before surgery—have a significantly higher risk of complications and mortality ^[18]. Many babies will still have complex medical needs, like feeding tubes or breathing support, after recovering from surgery ^[19][20].
• Palliative Care: A pediatric palliative care team provides an essential layer of support. They can be involved from the moment of diagnosis and work alongside cardiology and surgery teams ^[11]. Their focus is on managing symptoms, maximizing your baby’s comfort, and helping your family navigate difficult choices. Studies note that when parents are fully supported in shared decision-making—whether they choose surgery or comfort-focused medical care—they often feel their chosen path aligned with their goals, even though making these choices remains profoundly difficult ^[12].

Warning Signs: When to Seek Help

If your baby is being managed at home, your cardiology team will provide specific safety instructions. In general, you should seek urgent medical help if you notice signs of worsening heart failure or pulmonary hypertension:

• Severe or worsening breathing effort (breathing very fast, grunting, or sucking in at the ribs)
• A blue or gray color (cyanosis) that is new or worse than your baby’s baseline
• Pauses in breathing (apnea)
• Unusual unresponsiveness or extreme lethargy
• Marked exhaustion or sweating during feeds, or an inability to feed
• Substantially fewer wet diapers than usual