How early can CHD be detected in pregnancy?
Congenital Heart Disease (CHD) can be detected as early as 11 to 14 weeks of pregnancy through specialized first-trimester fetal echocardiography. While the standard NHS 20-week anomaly scan remains the gold standard for a comprehensive diagnosis, high-resolution transvaginal and transabdominal ultrasound now allow clinicians to identify major structural defects during the late first trimester. Early detection is particularly effective for severe cardiac malformations, with some specialized centres reporting a sensitivity of up to 100% for critical lesions during this early window.
The advancement of ultrasound technology has significantly shifted the timeline for prenatal cardiac assessment. Traditionally, families had to wait until the midpoint of pregnancy to receive a detailed evaluation of the fetal heart. However, for pregnancies identified as high-risk due to factors such as increased nuchal translucency, a family history of heart defects, or maternal conditions like diabetes early screening offers a vital opportunity for early counselling and specialized care planning. This proactive approach ensures that any necessary medical interventions can be prepared well in advance of the delivery.
What We’ll Discuss in This Article
- The timeline of heart development and early detection windows
- The role of first-trimester fetal echocardiography (11–14 weeks)
- Difference between transabdominal and transvaginal ultrasound approaches
- Key indicators that trigger an early cardiac referral
- The accuracy and limitations of early screening compared to the 20-week scan
- Genetic screening (NIPT) and its association with heart defect risks
The Timeline of Early CHD Detection
Major structural heart defects can often be detected between 11 and 14 weeks of gestation using specialized fetal echocardiography. During this period, the fetal heart is roughly the size of a marble, yet high-resolution scanners can visualize the four chambers, the crossing of the great arteries, and the heart rhythm. According to clinical data from the European Heart Journal, Guo, H., et al. (2025). ‘First trimester maternal infections and offspring congenital heart defects: a meta-analysis.’ , first-trimester screening is increasingly effective in diagnosing severe CHD, which helps families make informed decisions earlier in the pregnancy.
The following table summarizes the detection milestones during different stages of pregnancy:
| Pregnancy Stage | Gestational Weeks | Primary Screening Tool | Detection Capability |
| First Trimester | 11 – 14 Weeks | Early Fetal Echo (TVUS/Abdominal) | Severe/Major structural defects |
| Early Second Trimester | 15 – 17 Weeks | Targeted Fetal Echocardiogram | Refinement of first-trimester findings |
| Standard Screening | 18 – 22 Weeks | 20-Week Anomaly Scan | Gold standard for all structural CHD |
| Late Second Trimester | 24 – 28 Weeks | Follow-up Fetal Echo | Evolving lesions (e.g., coarctation) |
While early scans are highly effective for major malformations, they cannot replace the comprehensive 20-week study. Some smaller defects, such as minor holes in the heart walls or mild valve narrowings, may only become visible as the heart grows larger and its structures become more distinct.
Methods of Early Detection: TVUS and Abdominal Scans
To achieve the best possible images during the early stages, clinicians often use a combination of transabdominal and transvaginal ultrasound (TVUS). Transvaginal ultrasound allows the probe to be closer to the uterus, providing superior resolution for the tiny fetal heart at 12 or 13 weeks. This method is particularly helpful if the transabdominal view is limited by the mother’s body habitus or the position of the fetus.
- Transabdominal Ultrasound: The standard method used for most prenatal scans. It provides a good overview of the baby’s development but may lack the fine detail needed for the heart before 15 weeks.
- Transvaginal Ultrasound: Uses a smaller probe inserted into the vagina. This is the preferred method for ‘Early Fetal Echo’ as it produces clearer images of the heart’s internal plumbing in the first trimester.
- Doppler Technology: Used alongside both methods to measure the direction and speed of blood flow, helping to identify leaks or blockages in the heart’s valves and vessels.
Indications for Early Cardiac Screening
Not every pregnancy requires a specialized heart scan at 12 weeks. In the UK, early referrals are usually reserved for cases where the risk of CHD is statistically higher than average. A primary trigger is an increased ‘nuchal translucency’ (NT) measurement the fluid at the back of the baby’s neck noted during the dating scan. An NT measurement above 3.5mm is strongly associated with heart defects, even if the baby’s chromosomes are normal.
Other triggers for an early fetal echo include:
- Maternal Diabetes: Pre-existing Type 1 or Type 2 diabetes increases the risk of fetal cardiac malformations.
- Family History: Having a previous child or a parent with a congenital heart defect.
- Genetic Risks: Findings from Non-Invasive Prenatal Testing (NIPT) that suggest a chromosomal disorder.
- Conception via IVF: Clinical data indicates a slightly higher incidence of CHD in pregnancies conceived through assisted reproduction.
To Summarise
Congenital Heart Disease can be identified as early as 11 to 14 weeks in specialized clinical settings, particularly for severe and critical defects. While early fetal echocardiography provides invaluable reassurance or early diagnosis for high-risk pregnancies, it serves as a supplement to, rather than a replacement for, the detailed 20-week anomaly scan. A multi-layered approach involving early ultrasound, genetic screening, and mid-pregnancy confirmation ensures the highest level of accuracy for prenatal heart care.
If you are concerned about your baby’s heart development or have a known risk factor, speak with your midwife or consultant about a referral for an early fetal echocardiogram.
If you experience severe abdominal pain or heavy bleeding during pregnancy, call 999 immediately.
Can a 12-week scan see a hole in the heart?
Very large holes in the heart walls can sometimes be seen at 12 weeks, but most common holes (VSDs) are too small to be detected until later in pregnancy.
Is NIPT the same as a heart scan?
No, NIPT is a blood test that screens for chromosomal conditions like Down’s syndrome. While these conditions are linked to heart defects, the test cannot see the heart’s structure.
Does a normal early heart scan mean the baby is 100% fine?
A normal result is very reassuring for major defects, but a repeat scan at 20 weeks is always necessary to check for evolving or smaller issues.
Is transvaginal ultrasound safe for the baby?
Yes, it is a safe and common procedure that uses sound waves and does not pose a risk to the pregnancy.
Why did my sonographer suggest a repeat scan at 24 weeks?
Some conditions, like the narrowing of the main artery (aorta), can progress as the baby grows, so a follow-up is needed to ensure the blood flow remains healthy.
Can fetal echocardiography detect heart rhythm problems?
Yes, specialists can use the scan to monitor the heart’s rhythm and detect if the heart is beating too fast, too slow, or irregularly.
What is the ‘four-chamber view’?
This is a standard ultrasound view that shows the two upper and two lower chambers of the heart, which is the baseline check for structural health.
Authority Snapshot (E-E-A-T Block)
This article was reviewed by Dr. Stefan Petrov, a UK-trained physician (MBBS) with postgraduate certifications in ACLS and BLS. Dr. Petrov has extensive experience in general medicine and emergency care, having worked in hospital wards and intensive care units where prenatal and neonatal health are prioritized. His background in medical education ensures that this guidance on early CHD detection aligns with the latest 2025 clinical meta-analyses and NHS standards.
