Screening for congenital heart disease

One of the prerequisites of screening is that the test applied is both highly sensitive and specific for the condition. Ultrasound screening at 18–20 weeks of gestation detects at least 85% of spinal and renal abnormalities in the fetus, and yet overall only 23% of structural cardiac abnormalities were detected in the United Kingdom survey.3 4 If the public were aware of this low sensitivity compared with screening for other conditions, would the rate of cardiac diagnosis be deemed acceptable? I doubt it.

Screening is applied to populations to delineate a high risk group that may be offered a diagnostic procedure. However, it is not clear which pregnancies are at increased risk of cardiac malformation as the majority of babies with congenital heart disease are born to mothers with no discernible risk factors. This makes selective screening difficult. Currently recognised high risk groups are shown in table 1.

Referral because of a suspected cardiac abnormality detected at the 20 weeks scan may yield a true abnormality in 70% of cases, while referral because of a family history of congenital heart disease, or of maternal disease such as diabetes mellitus, usually only detects an abnormality in 2% of referred cases. Clearly it will be difficult to select out those who most require a specialist fetal cardiology examination unless substantial improvements are made in first line screening of the entire pregnant population. Earlier biochemical or physical markers of congenital heart disease such as an increased nuchal fold measurement at 11–14 weeks may help to define the high risk group further.5

Current monitoring practice

The opportunities for antenatal detection of congenital heart disease occur at a woman's local hospital rather than in specialist centres. Table 2 indicates the gestational age at which antenatal tests are performed and why a woman may be referred for a fetal cardiac examination.

A fetal echocardiography service is available through the 17 specialist centres for paediatric cardiology in the United Kingdom. There are different practice patterns, with a handful of cardiologists specialising in fetal cardiology who work in large fetal medicine/obstetric units and link to the paediatric cardiology unit in a “hub and spoke” fashion (such as that practised at the Royal Brompton and Harefield Hospital). I would propose this as a best practice model as it permits a comprehensive assessment of the fetus by a variety of fetal specialists working together. This improves diagnosis and communication and is usually more convenient for the patient. Antenatal consultation with the neonatal and cardiac team, including the surgeon, can be arranged to discuss the surgical options and plan the perinatal care.

If there is inequality of access to the perinatal cardiology service, where does it lie? Clearly a failure to detect a cardiac problem during the screening procedures reduces referral to the third line examiners (those practising fetal cardiology) and may put a newborn baby's life at risk. In areas where there is enthusiasm for fetal cardiac screening the detection rate in referral obstetric units is above average.6 7

Does an antenatal diagnosis of congenital heart disease benefit the child?

Cost-effectiveness of screening for fetal cardiac malformations cannot easily be demonstrated except where women choose termination of pregnancy when a complex heart problem is diagnosed. Some series have shown a worse outcome for those babies with an antenatal diagnosis.8 This in part reflects selection bias, in that the worst cases are more likely to be detected before birth. However, it also shows that careful perinatal management can result in the safe transfer of infants with difficult circulations to the cardiac unit in good condition for surgery, who might otherwise have died before arrival.

There is evidence now that the detection of certain conditions before birth, such as transposition of the great arteries, results in an improved outcome, as those with a restrictive oval foramen can be managed appropriately in the first hours after birth.9 In addition, antenatal recognition of infants who will have a duct dependent circulation after birth enables safe management, preventing neonatal collapse and possible cerebral injury before cardiopulmonary bypass. The costs of preventable cerebral damage to the individual, the family, and the health authority cannot be overestimated.

An antenatal diagnosis may result in rather more intangible benefits for the family. It allows time for the family to learn about and to appreciate the baby's condition and understand the implications for the future of both the child and the family. It permits time for further investigations, including exclusion of chromosomal problems such as 22q11 deletion that may affect management strategies at the time of cardiac surgery,10 and for a second opinion if required. In general, an antenatal diagnosis creates a more informed, supportive environment for the child.

The way forward

Several steps could be implemented to improve the rate of detection of congenital heart disease before birth.

• Sonographers—Cardiac malformations can be detected by a series of five transverse cuts incorporated into the 20 minute anomaly scan (figs 1-5) Additional teaching material can be provided and feedback mechanisms could ideally be set in place between individual sonographers and their cardiac referral centres. It is important to ensure that equipment used for the cardiac examination is of sufficient quality with fast frame rates in order to appreciate the fast moving fetal cardiac structures.

• Obstetricians and specialist registrars—Fetal cardiac training should be incorporated into obstetric specialist registrar training schemes so that all obstetricians with an interest in ultrasound are competent to supervise sonographers and to provide assistance in cases of suspected cardiac anomaly. It is useful for the perinatal cardiologist to have a good relationship with these obstetricians and to be available to clarify structural abnormalities and to teach. A shared clinic greatly improves the diagnostic skills of both parties and facilitates management of the individual fetus.

• Audit—Audit is essential to assess the effectiveness of intervention on training. It is still not clear how many women are offered an anomaly scan in the United Kingdom, or the percentage who take advantage of this. Examination of the fetal cardiovascular system varies widely from centre to centre, and standardisation of technique might ensure a more uniform detection rate throughout the United Kingdom.

Support and information for families

Any increase in antenatal diagnosis should be accompanied by an increased ability to provide information and support for families, so that they can decide what is right for them. Support mechanisms are provided jointly by genetic counsellors and health professionals but are sometimes disjointed and ineffective. A cohesive approach is essential to improve the situation and to provide families with the information and support essential to a satisfactory experience whatever the eventual outcome.