A congenital heart defect is a problem in the structure of the heart that is present at birth. Signs and symptoms depend on the specific type of problem. The defect can vary from minor to life-threatening. Approximately one out of every 100 live born infants (~1 percent) will be born with a congenital heart defect, which usually develops during the embryologic formation of the heart (first trimester).

These defects can be straightforward, such as a hole in the heart connecting two chambers (atrial or ventricular septal defect) or an abnormal heart valve (pulmonary or aortic stenosis).

They can also be more complex defects in which a major portion of the heart does not form (such as hypo plastic left heart syndrome) or the anatomic connections are abnormal (such as transposition of the great arteries).

Some infants will be born with a heart defect that requires immediate stabilization of the baby shortly after birth, followed by surgery.

Both genetic and environmental factors are suspected in the formation of congenital heart disease. Specific gene defects (22q11 deletion, trisomy 21) have been identified as having a very strong association between congenital heart disease and more generalized syndromes. In addition, there are other factors such as maternal diabetes, and specific medications (such as anticonvulsants) that have been associated with increased rates of heart defects.

The ultrasound study includes two-dimensional imaging, 3-dimensional imaging, colour flow, and Doppler evaluation of blood flow. After the study is performed, the patient is counselled by the Foetal Medicine Specialist on the diagnosis and prognosis.

The test is either performed from above (abdominal) or through the vagina (transvaginal). As in the routine pregnancy tests, a sound wave is transmitted that is reflected by the baby’s heart and is captured to project an image of the heart on the screen. This helps the Fetal Medicine Special is to better see the structure and function of the unborn child's heart.

The main observations that would be made during the course of the scan procedure would be the structure of the heart, blood flow and beating rhythm.

Some factors such as maternal lupus require several studies to be conducted even if the first one is normal. There also may be a structure that is not seen as well as the doctor would like due to the position of the baby and the patient may be asked to return even though the suspicion of a problem is low. Even in the case of a totally normal, high quality study, not all heart problems can be ruled out. This is because the circulation in the fetus changes after birth. Additionally, very small holes between the lower chambers of the heart are hard to see.

Fetal echocardiograms can reliably be performed any time after 17–18 weeks gestation; however if scanning is done before 18 weeks, the patient will likely be asked to return for more definitive pictures to confirm the findings on the early study.

The diagnosis of a heart defect has significant implications for the overall health of the fetus; certain heart defects may significantly increase the risk of genetic problems such as Down’s Syndrome. The finding of benign tumors in the heart makes the diagnosis of Tuberous Sclerosis, a genetic syndrome that has significant implications for abnormal brain development much more likely.

Pregnancies may be at risk for congenital heart disease for a variety of fetal, maternal or familial reasons.

• An abnormal appearing heart
• Abnormal heart rate or arrhythmia on routine screening ultrasound
• Aneuploidy (chromosomal abnormality)
• Increased nuchal translucency thickness at first trimester evaluation
• Non-cardiac foetal structural abnormalities
• A two-vessel umbilical cord
• Twins
• Fluid accumulation in the fetus
• If the unborn baby has been diagnosed with a genetic abnormality including disorders with abnormal number of chromosome; Down syndrome, for example
• If a heart abnormality is suspected on routine ultrasound
• If there are abnormalities outside of the heart of the fetus noted on routine prenatal ultrasound; examples include extra fluid around the lungs or the heart or an abnormality of another organ such as the kidneys or brain.
• Abnormal fetal heart rate or rhythm. This can be an irregular heartbeat or heart rate that is too fast or too slow.

• Maternal diabetes, lupus or other systemic disease that involves the heart (such as DiGeorge Syndrome)
• First-trimester use of known teratogens
• IVF pregnancies
• Maternal congenital heart disease
• If the mother has taken medications that are known to cause congenital heart defects.
• If the mother has specific health problems such as diabetes (the type that the mother had prior to pregnancy)
• If the mother had specific infections during pregnancy such as rubella or CMV

• If a first degree relative has been diagnosed with a congenital heart defect. First degree relative includes the mother or father of the baby as well as any siblings of the baby
• If there is a known family history of disorders that are passed along from generation to generation such as Marfan's syndrome or tuberous sclerosis

While fetal medicine specialists work to detect defects to the maximum extent possible, it must be realized by the patient and her family that imaging procedures cannot detail extremely minor portions of the heart. Heart defects often develop over time such as those that affect the heart muscles or valves.