Understanding CHD: How It Happens and Who’s Most at Risk

 Congenital heart defects (CHD) are the most common birth defects worldwide, affecting nearly 1 in every 100 babies. For many parents, the diagnosis arrives suddenly—during a prenatal ultrasound, shortly after birth, or even later in childhood when symptoms begin to appear. But CHD does not begin at birth; it begins far earlier, during the earliest weeks of pregnancy when the baby’s heart is still forming.

Understanding how CHD happens and who is most at risk empowers parents, caregivers, and families to make informed decisions, seek early diagnosis, and ensure the best possible outcomes for their children.

This article breaks down the science of CHD in clear, parent-friendly language and explores the latest understanding of risk factors, causes, and prevention insights—based on current research and 2025 medical guidelines.

1. What Exactly Is a Congenital Heart Defect?

Congenital heart defects are structural problems in the heart that develop before birth. They can affect:

• The walls of the heart
• The valves
• The major blood vessels
• The way blood flows through the heart

Some defects are mild and require little or no treatment. Others are serious and require surgery or catheter procedures.

CHD ranges widely, including:

• Septal defects (holes in the heart such as VSD or ASD)
• Valve abnormalities (stenosis or regurgitation)
• Transposition of the great arteries (TGA)
• Tetralogy of Fallot (TOF)
• Single-ventricle defects like HLHS
• Coarctation of the aorta

What all CHDs have in common is that they form early—before most people even know they’re pregnant.

2. How and When Does CHD Develop?

The heart begins forming just weeks after conception, often before week 6 of pregnancy. It starts as a simple tube, then twists, folds, and divides into chambers, valves, and vessels.

CHD occurs when this complex process is disrupted.

Common causes of disruption include:

• Genetic variations
• Environmental exposures
• Maternal health conditions
• Placental abnormalities
• A combination of factors (most common)

In fact, experts estimate that 80% of CHD cases result from several small factors interacting, rather than one single cause.

3. The Genetic Roots of CHD: It’s Not Always Inherited

Many parents wonder if CHD is their fault. The answer is almost always no.

How genetics contribute:

• Some cases of CHD are linked to genetic syndromes, such as:
  • Down syndrome
  • DiGeorge syndrome (22q11.2 deletion)
  • Turner syndrome
• Some are caused by single-gene mutations or small chromosomal changes.
• Most cases involve multiple gene variations acting together, not a single inherited problem.

Is CHD inherited?

Sometimes yes, but usually no.

• The risk of having another child with CHD is approximately 2–6%, slightly higher if:

  • A parent has CHD
  • More than one sibling has CHD
  • The defect is part of a genetic syndrome

Genetic testing is now recommended in many CHD diagnoses because it helps uncover:

• The likelihood of recurrence
• Other potential health concerns
• The best long-term care strategy

Important: Even if a genetic link is found, parents nearly always did nothing to cause it.

4. Environmental Factors: What Happens During Pregnancy Matters

The environment inside the womb plays a major role in fetal development. Certain prenatal exposures have been linked to increased CHD risk.

4.1 Maternal illnesses

Some conditions increase the chance of a heart defect, especially if not well controlled:

• Diabetes
• Phenylketonuria (PKU)
• Autoimmune diseases (e.g., lupus)
• Rubella and other viral infections during pregnancy

4.2 Medications and chemical exposures

Some medications are known to increase CHD risk if taken during early pregnancy, such as:

• Certain acne medications
• Anti-seizure medications
• Some mood-stabilizing drugs

Women planning pregnancy or who may become pregnant should always consult a doctor before stopping or changing any medication.

4.3 Alcohol, drugs, and smoking

These exposures are linked with higher rates of congenital defects, including CHD.

4.4 Maternal age and reproductive technology

Advanced maternal age and assisted reproductive technologies (IVF/ICSI) have a slightly higher association with CHD, although the reason isn't fully understood.

5. The Role of the Placenta: A Hidden Factor in CHD Development

Recent research highlights the placenta as a major contributor to congenital heart development. Since the placenta and the heart form around the same time, problems in placental development may influence:

• Blood flow to the fetus
• Nutrient and oxygen delivery
• Overall fetal organ development

Studies show that placental abnormalities are more common in pregnancies involving CHD, suggesting that the placenta and the fetal heart are more connected than previously thought.

6. Who Is Most at Risk for CHD?

While CHD can happen in any pregnancy, certain families and situations have a higher risk.

6.1 Families with a CHD history

Risk increases if:

• A parent has CHD
• A sibling has CHD
• Multiple relatives had CHD
• The previous child had a severe or genetic-related CHD

6.2 Mothers with chronic health conditions

Higher risk is seen in mothers who have:

• Diabetes (especially poorly controlled)
• Obesity
• Hypertension
• Autoimmune disorders
• Thyroid disease

6.3 Certain maternal exposures

• Viral infections (especially in the first trimester)
• Alcohol or drug use
• Smoking
• Exposure to chemical toxins

6.4 Pregnancies conceived through assisted reproductive technology

While still relatively low risk, IVF pregnancies show a slightly increased rate of CHD, possibly related to embryo development or parental genetics.

6.5 Prematurity

Preterm babies have a higher rate of CHD, though it’s unclear whether CHD leads to early delivery or prematurity contributes to heart defects.

7. Can CHD Be Prevented?

There is no guaranteed way to prevent CHD. However, certain steps may help lower risk.

Before pregnancy:

• Maintain a healthy weight
• Manage chronic health conditions
• Take folic acid or prenatal vitamins
• Avoid alcohol and smoking
• Discuss medications with a doctor

During pregnancy:

• Get early prenatal care
• Manage blood sugar and blood pressure
• Avoid harmful exposures
• Get vaccinated (rubella, flu, etc.)
• Maintain a healthy diet

These steps support overall fetal development—but they cannot eliminate CHD risk entirely.

8. How Early Can CHD Be Detected?

Thanks to modern technology, CHD can be detected earlier and more accurately than ever before.

Prenatal detection

• Standard ultrasounds between 18–22 weeks can identify many structural defects
• If anything looks abnormal, a fetal echocardiogram is recommended.
• High-risk mothers may be offered fetal echo even without symptoms.

Newborn screening

Nearly all hospitals now use pulse oximetry screening to detect critical heart defects shortly after birth.

Postnatal diagnosis

Some mild defects aren’t discovered until later in childhood when symptoms appear:

• Fast breathing
• Poor weight gain
• Fatigue
• Bluish skin (cyanosis)
• Frequent respiratory infections

Early detection leads to better outcomes regardless of when diagnosis occurs.

9. Why Some Children With CHD Are at Higher Risk of Complications

Not all CHDs are equal. Several factors influence how serious a defect may be:

• Type of CHD (holes vs. valve issues vs. complex defects)
• Severity (small vs. large defects)
• Associated genetic conditions
• Prematurity
• Overall health of the baby
• Access to specialized cardiac care

Children with complex CHDs like HLHS, TGA, or TOF require more intensive monitoring and intervention.

10. What This Means for Families: Hope and Realistic Expectations

Although CHD is the most common birth defect, survival and long-term outcomes have improved more in this field than nearly any other area of pediatric medicine.

Today:

• Over 90% of CHD children survive to adulthood.
• Many live full, active lives.
• Lifelong care ensures good quality of life.

Parents should remember:

• CHD is no one’s fault.
• Many cases happen without any identifiable cause.
• You are not alone—millions of families share this journey.

The combination of earlier diagnosis, better surgical techniques, safer catheter-based interventions, and lifelong heart care means that children with CHD in 2025 have brighter futures than ever before.

 Knowledge Is Power in the CHD Journey

Understanding how CHD happens and which factors increase risk helps families navigate the emotional and medical challenges of diagnosis. While CHD can’t always be prevented, awareness allows for early detection, proactive care, and informed decision-making.

Whether your child has a minor defect requiring monitoring or a complex CHD needing surgical care, modern medicine offers powerful tools and hope. With the right support and information, families can face CHD with strength, clarity, and confidence.