Antenatal screening for congenital heart disease

• antenatal screening and congenital heart disease
  • cardiac malformations are one of the commonest types of congenital abnormality and remain an important cause of morbidity and mortality in infancy
    • almost all major forms of congenital heart disease (CHD), as well as some minor forms, can be detected during fetal life by ultrasound examination with a high degree of diagnostic accuracy in experienced centres
    • detection of CHD in early pregnancy allows parental choice on the course of the pregnancy and time to prepare for the likely course of events if the pregnancy progresses to delivery
    • normal fetal heart scan can provide reassurance to parents at high risk of having a child with CHD
  • High Risk pregnancies
    • maternal factors that increase the risk of CHD include:
      • family history of CHD
        • other siblings with CHD
          • if one previous child has had CHD the risk in any subsequent pregnancy is 2-3%
            • if two children with CHD the risk increases to about 10%
        • if parent with CHD
          • if parent has history of CHD then the risk to the next generation is 1.5-3%
        • other maternal risk factors
          • maternal diabetes is associated with a 2-3% risk of cardiac malformation -good diabetic control in early pregnancy is thought to diminish this risk
          • exposure to teratogens, such as oral anticoagulants and antiepileptics, in early pregnancy is reported to be associated with a 2% risk of heart malformation
        • fetal risk factors associated with CHD include:
          • an extra-cardiac fetal anomaly on ultrasound
          • fetal arrhythmias. Some fetal arrhythmias, particularly complete heart block, are associated with structural heart disease
          • non-immune fetal hydrops may be due to CHD
          • increased nuchal translucency in the first trimester
            • associated with a high risk for CHD, even when the fetal karyotype is normal
  • Low Risk Pregnancies
    • most cases of CHD occur in low risk groups and can only be detected during obstetric screening
    • four-chamber view of the fetal heart can detect some severe forms of cardiac malformation prenatally and imaging of the arterial connections greatly improves the detection rate
    • the success of prenatal screening for CHD is very dependent to the expertise and experience of the sonographer which is not uniform across the UK
  • fetal cardiology scans
    • fetal cardiology scans can be performed from 13-14 weeks gestation in specialist centres, though the majority of cases are seen between 18-23 weeks of gestation
      • can detect most major structural abnormalities of the heart, abnormalities of cardiac function and rhythm disturbances, such as supraventricular tachycardia, atrial flutter and congenital heart block
      • abnormalities that are not easily detectable/undetectable via fetal cardiology scans
        • secundum atrial septal defects and a persistent arterial duct will only become evident after birth and small ventricular septal defects may be missed
        • milder forms of obstructive lesions of the aorta and pulmonary artery may be undetectable during fetal life
  • if diagnosis of CHD
    • because there is a high association between CHD and other anomalies, it is important to consider further investigations, such as amniocentesis, to exclude conditions such as trisomy 21 (Down's syndrome) - which is likely to be present in 50% of cases of atrioventricular septal defect, or other potentially lethal chromasomal abnormalities
    • major decision the parents face when a severe cardiac defect is diagnosed in early pregnancy is whether or not to terminate it
    • for continuing pregnancies, the advantage of prenatal diagnosis is that it allows multidisciplinary perinatal management and immediate cardiac assessment of the neonate to be planned
      • if appropriate, delivery can be arranged in a centre with on site paediatric cardiology facilities

Reference:

• 1. British Heart Foundation (May 2009). Antenatal screening for congenital heart disease.