A Health Surveillance Update on Canadian Children and Youth

Neural Tube Defects

The importance of neural tube defects lies both in the disability and death they cause, as well as the opportunities to address their occurrence through primary prevention.

Congenital anomalies or birth defects are a leading cause of all infant deaths and one of the top 10 causes of potential years of life lost.⁽¹⁴⁾ Neural tube defects (NTDs) are one important category of birth defects that result from the failure of the neural tube to close during the early embryonic development. They include anencephaly, spina bifida and encephalocoele.⁽¹⁵⁾ The importance of NTDs lies both in the disability and death they cause, as well as the opportunities to address their occurrence through primary prevention. There is evidence that multivitamin supplements containing folic acid, taken periconceptionally, reduce the risk of NTDs.⁽¹⁶⁾ The NTD rate is normally presented as a birth prevalence that consists of the number of affected infants (live births and stillbirths) per 1,000 total births (live birth and stillbirths).

In Canada (excluding Quebec) in 1996, the birth prevalence of NTDs was 0.77 per 1,000, or 219 affected infants.⁽¹⁷⁾ These 219 cases resulted in 223 related anomalies - 33 anencephalic, 160 spina bifida, and 30 encephalocoele. The number of NTDs exceeds the number of affected infants, as one infant may be affected by more than one NTD.

As depicted in Figure 5, the birth prevalence of NTDs in Canada has been declining gradually. In 1989, the rate was 1.1  per 1,000 total births compared with 0.77 per 1,000 total births in 1996. Decreases in the birth prevalence of NTDs may be partly due to increases in antenatal detection and subsequent termination of affected pregnancies.⁽¹⁸⁾ Other factors, such as better diets and more widespread use of vitamin supplementation, may have also contributed to the decline.⁽¹⁹⁾

There are variations in the NTD rate between and within nations. Canada's 1996 rate of 0.77 per 1,000 compares with a higher rate of 1.35 per 1,000 in the United Arab Emirates and lower reported rates of 0.13, 0.24, 0.35 and 0.62 per 1,000 in England/Wales, Israel, Finland and Norway respectively.⁽²⁰⁾ The causes for this international variation are poorly understood. Access to antenatal diagnosis and termination of NTD-affected pregnancies may explain some of the observed variation. In data from England and Wales, 319 NTDs were reported in terminated pregnancies in addition to the 86 anomalies that are included in the comparison rate. In contrast, in the United Arab Emirates, where termination of pregnancy is not permitted, all identified anomalies are included in the comparison rate. Figure 6 presents the 1996 NTD rates for Canada and several other countries. The Canadian NTD rate presented is derived from the number of affected infants, whereas the comparative international rates are based on the number of NTD anomalies. Analysis of the 1996 Canadian data reveals minimal variation in the rate based on affected infants versus number of anomalies (0.77 versus 0.79).

* 1989-1995 excluding Nova Scotia, 1996 excluding Quebec
Source: Bureau of Reproductive and Child Health, LCDC⁽¹⁷⁾

* excluding Quebec
Source: International clearinghouse for birth defects monitoring systems, 1998, except Canada: Bureau of Reproductive and Child Health, LCDC⁽¹⁷⁾

Data limitations
One of the major limitations in tracking congenital anomalies is the absence of mandatory and standardized national reporting of anomalies that are detected antenatally and result in the termination of the affected pregnancy. A failure to account for these cases will result in an underestimate of the true NTD rate and limit the interpretations of time trend data. As well, the availability of data from different regions in Canada varies over recent years, also limiting the comprehensiveness and consistency of the time trend analysis.

Summary
NTDs remain an important public health problem. Enhanced surveillance of NTDs that result in termination of pregnancy will ensure that future rates and trends are interpreted correctly. As primary prevention strategies continue, accurate analysis of NTD rates will be essential in evaluating public health efforts.

Unless referenced otherwise, neural tube defect statistics are the product of the Bureau of Reproductive and Child Health, LCDC.⁽¹⁷⁾

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