Overview

A congenital anomaly is a defect that is present at birth, and can result from either genetic or environmental factors, or both. Some congenital anomalies require ongoing treatment, and all present a reason for concern. Congenital anomalies are second to perinatal conditions as the leading cause of infant mortality and stillbirths. In British Columbia in 2000, congenital anomalies were responsible for a fifth of all infant deaths (age at death less than one year old) and nearly a tenth of all stillbirths.

Congenital anomalies are caused by gene mutations. These mutations may be inherited from a parent, result from errors during cell division, or result from events during or after conception. Specific drugs, especially when taken in a particular trimester, radiation exposure, certain viruses, and maternal use of alcohol and tobacco have all been identified as factors associated with congenital defects, and recent years have seen increased investigation into the possible effects of other environmental factors. Chromosomal abnormalities also result when meiosis and mitosis are not completed in a normal fashion. If both parents have an abnormal genetic trait their child will carry or manifest the defect. In affected families, the risk of occurrence of congenital defects increases with each child. Certain genetic diseases have also been found to occur more frequently within populations from specific ethnic backgrounds; for example, sickle cell anemia is particularly common among people whose ancestors come from sub-Saharan Africa.

A large range of genetic and environmental factors can produce the congenital anomalies reported in this publication.

• Congenital nervous system defects include anencephaly, neural tube defects, and microcephalus. Although there is a familial tendency in occurrences of many neural tube defects, multiple environmental factors also seem to be involved, particularly with anencephaly. Microcephaly may be the result of a chromosomal abnormality, a virus, or acquired through association with maternal herpes, ischemic insults, or hypothyroidism.
• Congenital anomalies of the heart include some defects associated with syndromes, such as trisomy 21 and Turner’s, as well as defects associated with maternal rubella, maternal anticonvulsant medication, or maternal alcohol consumption.
• Factors reported in the literature associated with cleft lip and cleft palate have included genetics, corticosteroids, radiation, hypoxia in utero, maternal viral illness, and dietary influences.
• Chromosomal anomalies are often associated with an advanced maternal age.

The grouping of congenital anomalies used in this report was selected on the basis of similar system development and to provide sufficient numbers to enable analysis. Subgroups were selected to reflect either the most serious conditions (where numbers warranted) or the most common within the group. The congenital anomalies classification categories represent conditions with a wide range in level of severity of impairment, disability, or disfigurement. The complete list of groups and subgroups with ICD codes is provided in Appendix 1.

• Neural tube defects include spina bifida, meningocele, and encephalocele.
• An anomaly of the eye can range in severity from complete agenesis (absence) to aphakia (absence of the lens), coloboma (absence or defect of ocular tissue), or ptosis (drooping) of the lid. Congenital cataract and entropion (inversion of the margin of the eyelid) are among the most frequently reported conditions in this group.
• Defects of the ear, face and neck include for example, anomalies that cause hearing impairment, branchial cleft cyst, webbing of neck, and macrostomia (greatly exaggerated width of the mouth); conditions with a wide range of impairment. The most common conditions in this group, preauricular skin tags or deformities of the pinna, are relatively less disabling.
• Other anomalies of the heart include, for the most part, unspecified heart defects, heart valve anomalies, or dextrocardia (location of the heart in the right hemithorax).
• Other circulatory system anomalies include defects of the aorta, pulmonary arteries, or peripheral circulation, and possible most often, single umbilical artery.
• While agenesis, and more commonly, hypoplasia (incomplete development) of the lung or larynx/trachea/bronchus atresia represent a small portion of Respiratory System Anomalies, choanal atresia (absence or closure of the openings between the nasal cavity and the nasopharynx) is probably more frequently reported.
• The most frequently reported anomalies of genital organs are undescended testicles and hypospadias.
• Anomalous conditions of the integument such as hemangioma (a benign tumour made of blood vessels), strawberry nevus, or epidermolysis bullosa can be severely disfiguring but the vast majority of conditions reported in this category are ill-defined birthmarks or skin tags.

This section of the report provides an overview of the birth incidence of congenital anomalies in the province since 1970, as well as trends in birth incidence rates of selected congenital anomalies over the last decade. Table 2 shows the number of provincial births with specific congenital anomalies by diagnostic category for 1970-1980 (combined) and for each year from 1981-2000. Table 3 presents the same diagnoses aggregated to show four time periods spanning the last two decades as well as statistically significant trends over the 1981-2000 time period. Next a series of graphs presents three-year moving averages for the incidence of selected congenital anomalies from 1981-2000. Graphs are provided for:

• total diagnoses (all congenital anomalies)
• anencephalus and similar defects
• neural tube defects
• hydrocephalus
• ventricular septal defect
• patent ductus arteriosus
• cleft palate/cleft lip
• congenital dislocation of hip
• foot defects (varus, valgus, and clubfoot)
• finger defects (polydactyly/syndactyly)
• limb reductions
• Down’s syndrome

All this information provides a provincial overview prior to looking at the data for congenital anomalies by geographic areas within the province.

The reader is referred to Appendix 1 for the complete list of congenital anomaly categories and codes. Caveats affecting the data can be found in the Guide to Data Interpretation in the General Information section at the beginning of this report.

Provincial Highlights

As shown in Table 2, the Health Status Registry recorded 91,793 congenital anomaly diagnoses in 64,794 live births and stillbirths in British Columbia between 1970 and 2000. During this time period, between 1,300 and 2,800 total births (live births plus stillbirths) per year were reported with at least one major or minor congenital anomaly. The average number of diagnoses per case ranged from a low of 1.3 in 1979-1980, 1981, and 1982, to a high of 1.8 in 1998.

More than a quarter (27.5% or 25,281) of the congenital anomaly diagnoses were musculoskeletal deformities; the most common of these were foot defects (varus, valgus, and clubfoot) with 6,393 diagnoses and congenital dislocation of hip with 5,687 diagnoses.

Both anomalies of the heart (12.7%) and anomalies of the genital organs (10.8%) were responsible for more than a tenth each of the congenital anomaly diagnoses reported to the HSR (with 11,625 and 9,875 diagnoses respectively).

Trends in the incidence of selected congenital anomaly rates for total births are presented for 1981 to 2000 in Table 3, Appendix 3, and in Figures 1 through 12. In the graphs, solid lines show the confidence intervals around the rates, while a dotted line indicates the trend over the entire time period. Like the other information presented in this report, the trends are based on cases reported to the Health Status Registry. Thus the data should be interpreted as a summary of what is available in the Registry, not as complete statistics on the birth incidence of the diagnoses. The reader is reminded that the trends represent a combination of actual changes in birth incidence with variations in reporting to the HSR. More details are provided in the Guide to Data Interpretation section of this report.

The rate for total diagnoses of all congenital anomalies averaged 68.91 per 1,000 total births. The rates for total reported diagnoses decreased steadily in the 1980s. This was followed by a plateau, and then steady increases in the mid and late 1990s. There was no statistically significant overall increase or decrease in the rates of total reported diagnoses over the last two decades.

The average incidence rates for the subcategories of reported congenital anomalies are low. Congenital dislocation of hip, with a rate of less than five per thousand (4.35 per 1,000 total births), had the highest incidence rate. Anencephalus and similar defects, with fewer than three in ten thousand (0.25 per 1,000), had the lowest.

Anencephalus and similar defects, neural tube defects, hydrocephalus, and limb reductions showed statistically significant decreases over the 1981-2000 period. No statistically significant trends were noted for ventricular septal defect, patent ductus arteriosus, varus, vulgus, and clubfoot, and polydactyly and syndactyly. Cleft palate/cleft lip, congenital dislocation of hip, and Down’s syndrome showed statistically significant increases. Since the risk of chromosomal anomalies in the baby increases with advancing maternal age, the increase in Down’s syndrome might reflect increasing average age of mothers.