1.4 Congenital Anomalies - Definitions

Congenital anomalies comprise a wide range of abnormalities of body structure or function that are present at birth and are of prenatal origin. For efficiency and practicality, the focus is commonly on major structural anomalies. These are defined as structural changes that have significant medical, social or cosmetic consequences for the affected individual, and typically require medical intervention. Examples include cleft lip and spina bifida.

Major structural anomalies are the conditions that account for most of the deaths, morbidity and disability related to congenital anomalies (see Box 1.1 for a list of selected external and internal major congenital anomalies). In contrast, minor congenital anomalies, although more prevalent among the population, are structural changes that pose no significant health problem in the neonatal period and tend to have limited social or cosmetic consequences for the affected individual. Examples include single palmar crease and clinodactyly.

Major anomalies are sometimes associated with minor anomalies, which might be objective (e.g. preauricular tags) or more subjective (e.g. low-set ears). Box 1.2 represents selected external minor congenital anomalies frequently captured by different surveillance systems, but only when associated with any of the major anomalies under surveillance. For a more detailed listing of minor anomalies, please refer to Appendix B. Often, surveillance systems will collect information on specific syndromes that are multiple anomalies pathogenetically related due to a single cause – for example, genetic or environmental causes that are known to cause birth defects. Certain syndromes caused by infectious diseases are of special interest in many low- and middle-income countries . For a detailed listing of selected syndromes of infectious origin that are of public health significance, please refer to Appendix B.

When establishing a new congenital anomalies surveillance programme, the initial anomalies that are included can be limited to structural anomalies that are readily identifiable and easily recognized on physical examination at birth or shortly after birth. The list may vary, depending on the capacity and resources of the health-care system and surveillance programme, but typically includes major external congenital anomalies. Examples include:

• orofacial clefts,
• neural tube defects, and
• limb deficiencies.

In contrast, detecting the vast majority of internal structural anomalies (e.g. congenital heart defects, intestinal malrotation and unilateral kidney agenesis) requires imaging techniques or other specialized procedures that may not be available consistently. In some cases, internal anomalies have external manifestations that allow the observer to suspect a particular diagnosis, as is the case with the urethral obstruction sequence. Similar to collecting information on internal defects, collecting information on syndromes often requires gathering data from multiple sources such as laboratory, imaging or genetic testing. Therefore, collecting surveillance data on internal defects and syndromes is typically not recommended when first starting a surveillance programme.

Classification by developmental mechanism or clinical presentation can be important in surveillance, because the same congenital anomaly can have different etiologies. Futhermore, the distinction may be important both clinically and in etiological studies. Please refer to Appendix C for more information about the causes of congenital anomalies and their classification according to developmental mechanism and clinical presentation.