Can CHD be detected before birth? 

Yes, many congenital heart defects can be detected before a baby is born, primarily through routine prenatal ultrasound scans. In the UK, the 20-week anomaly scan is the most common time for heart issues to be identified. Early detection is crucial as it allows medical teams to plan for specialized care or surgery immediately after delivery, significantly improving outcomes for complex cases. 

What We will cover in this Article 

• The role of the 20-week anomaly scan in heart detection 

• What happens during a foetal echocardiogram 

• Why some defects are easier to spot than others 

• The benefits of early diagnosis for neonatal care 

• Accuracy rates of prenatal screening in the UK 

• Next steps if a heart defect is suspected during pregnancy 

Prenatal Screening in the UK 

In the UK, the NHS offers prenatal screening to all pregnant individuals to monitor the baby’s development. The primary tool for detecting heart defects is the mid-pregnancy ultrasound, commonly known as the anomaly scan. This scan is performed between 18 and 21 weeks of pregnancy and includes a detailed examination of the baby’s heart structure, including the four chambers and the major outgoing blood vessels. 

While this scan is highly effective, it is important to note that it may not detect all defects. Approximately 50% to 60% of all heart defects are currently spotted during this routine scan in the UK, though this rate is significantly higher for more severe or ‘critical’ conditions. 

The Foetal Echocardiogram 

If a sonographer identifies a potential issue during a routine scan, or if there is a known high risk (such as a family history of CHD), a referral is made for a foetal echocardiogram. 

What is a Foetal Echocardiogram? 

This is a specialised ultrasound performed by a paediatric cardiologist or a foetal medicine specialist. It provides a highly detailed, real-time look at: 

• The blood flow through the heart valves. 

• The rhythm and rate of the baby’s heartbeat. 

• The size and thickness of the heart chambers. 

• The connection of the major arteries (aorta and pulmonary artery). 

Unlike a routine scan, the echocardiogram focuses specifically on the cardiovascular system and can be performed as early as 18 weeks, though images are usually clearer after 20 weeks. 

Why Detection Varies by Defect 

Some heart defects are ‘duct-dependent’ or involve structural changes that are highly visible on ultrasound, while others are subtle or only become apparent after the baby takes their first breath. 

Comparison of Detection Difficulty 

Defect Type	Ease of Prenatal Detection	Reason
Hypoplastic Left Heart Syndrome (HLHS)	High	The left side of the heart is visibly smaller.
Transposition of the Great Arteries	Moderate	Requires a specific ‘outflow tract’ view.
Atrial Septal Defect (ASD)	Low	Small holes are normal in the womb (foramen ovale).
Coarctation of the Aorta	Low/Moderate	Narrowing often only becomes severe after birth.
Tetralogy of Fallot	High	Structural anomalies like VSD are often clear.

Benefits of Early Diagnosis 

Detecting a heart defect before birth is a significant advantage for both the medical team and the parents. It moves the diagnosis from an ’emergency’ situation at birth to a ‘planned’ clinical pathway. 

• Specialised Delivery: The birth can be scheduled at a hospital with a Level 3 Neonatal Intensive Care Unit (NICU) and paediatric surgical facilities. 

• Immediate Treatment: Certain medications, like prostaglandins, can be started immediately after birth to keep vital heart pathways open. 

• Parental Preparation: Families have time to meet with cardiologists, surgeons, and support groups like the British Heart Foundation. 

• Improved Outcomes: Research shows that babies with complex defects like Transposition of the Great Arteries have better survival rates when diagnosed prenatally. 

To Summarise 

Congenital heart disease is frequently detectable before birth through the routine 20-week NHS anomaly scan. While not every defect can be seen especially minor holes or conditions that develop as the baby grows the majority of critical defects are identified early. This allows for life-saving preparations and ensures the baby is delivered in the safest possible environment. 

If you experience severe, sudden, or worsening symptoms during pregnancy, such as reduced foetal movement or sharp pain, contact your midwife or call 999 in an emergency. 

Authority Snapshot (E-E-A-T Block) 

This article was reviewed by Dr. Stefan Petrov, a UK-trained physician with experience in general surgery and emergency medicine. Dr. Petrov’s clinical background, including his training in the UK Medical Licensing Assessment, ensures this information on prenatal screening meets current NHS and NICE standards. The content is designed to provide clear, evidence-based guidance for expectant parents navigating CHD screening.