Oral clefting in Canada : a temporal analysis for the period 1989-2000

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J Andrés León and Jocelyn Rouleau
Maternal and Infant Health Section, Public Health Agency of Canada

Introduction

This report presents a temporal analysis of oral clefting in Canada for the period 1989-2000. The analysis is based on national data from the Canadian Congenital Anomalies Surveillance System (CCASS). Percentage and prevalence (per 10,000 births) values for both isolated and non-isolated cases were calculated over the study period. Prevalence by sex and sex prevalence ratios were also calculated.

 Methodology

CCASS is a national population-based surveillance system that uses hospital administrative data. Hospital data from all provinces and territories, excepting Alberta and Quebec , are routinely collected by the Canadian Institute of Health Information (CIHI). CIHI’s Discharge Abstract Database (DAD) is CCASS’ primary source of data for congenital anomalies surveillance. Alberta and Quebec provide their data directly to CCASS.

CCASS captures registered stillbirths ≥ 20 weeks of gestation or ≥ 500 g, and live births ≥ 20 weeks up to one year of age. Spontaneous abortions and terminations, both elective and therapeutic, are not captured. CCASS covers approximately 97% of all live and stillbirths in Canada . Data from Nova Scottia for the year 1995 and earlier were not available through the DAD data set, therefore, they were not included in the analysis.

Oral clefts were grouped as cleft lip (CL), cleft lip and palate (CLP) and cleft palate (CP) according to the International Classification of Diseases (ICD) 9 th edition (CP: 749.0, CPL: 749.2, CL: 749.1). These cleft groups were mutually exclusive. The period of interest for the analysis was 1989-2000. The temporal analysis involved the calculation of percentage and prevalence values for both isolated and non-isolated cases by clefting group. Isolated cases were defined as clefts that ocurred alone and not associated with any other congenital anomalies, including minor ones. Non-isolated cases included both syndromic and non-syndromic clefts. Prevalence by sex and sex prevalence ratio (female to male) were also calculated. The prevalences were obtained by dividing the total number of cases identified in a given year (or during the 1989-2000 period) by the total number of births (e.g., live births and stillbirths) registered in Canada for the same year (or for the 1989-2000 period). Three hundred cases whose sex was not known were excluded from the analysis by sex.

Results

Between 1989 and 2000, there were 8,101 cases of oral clefting with a prevalence of 18.5 per 10,000 births (Table 1). Out of these, 5,118 cases (63%) were isolated and 2,983 (37%) were non-isolated clefts. CLP represented 41% (prevalence: 7.6) of all clefts whereas CP and CL represented 39% (prevalence: 7.3) and 19% (prevalence: 3.6), respectively. Isolated clefts accounted for 78% (prevalence: 2.8), 66% (prevalence; 5.0) and 53% (prevalence: 3.9) of CL, CLP and CP cases, respectively.

Table 1. Distribution and prevalence of all, isolated and non-isolated clefts by clefting type in Canada , 1989-2000.

Anomaly		Cases %		% all clefts	Prev*
Clefts
All		8,101		100.0	18.5
isolated		5,118		63.2	11.7
Non-isolated		2,983		36.8	6.8
Cleft lip
All		1,567	100.0	19.3	3.6
isolated		1,221	77.9		2.8
Non-isolated		346	22.1		0.8
Cleft lip and palate
All		3,337	100.0	41.2	7.6
isolated		2,200	65.9		5.0
Non-isolated		1,137	34.1		2.6
Cleft palate
All		3,197	100.0	39.5	7.3
isolated		1,697	53.1		3.9
Non-isolated		1,500	46.9		3.4
* Prevalence per 10,000 births

Graphs 1, 2 and 3 show the temporal distribution of clefts by group over the study period. Isolated clefts predominated over non-isolated clefts among CL and CLP cases although the proportion of isolated clefts was higher among CL than in CLP cases. (Graphs 1 and 2). The proportion of isolated vs. non-isolated clefts among CP cases was about the same (Graph 3).

Graph 1. Temporal distribution of all and isolated cases of cleft lip (CL) in Canada , 1989-2000.

 Graph 2. Temporal distribution of all and isolated cases of cleft lip and palate (CLP) in Canada , 1989-2000.

Graph 3. Temporal distribution of all and isolated cases of cleft palate (CP) in Canada , 1989-2000.

Graphs 4, 5 and 6 show the temporal distribution of oral cleft prevalence among all and isolated cases by clefting group over the study period. The prevalence of CL presented a decreasing pattern, which was more evident in the 1991-1994 and 1996-1999 periods (Graph 4). This decrease was mainly due to the decrease in the prevalence of isolated cases as that of non-isolated cases showed a rather small variation. Although there was a slight increasing pattern among CLP and CP cases between 1997 and 1999 and between 1996 and 1999 respectively, the prevalence among CLP and CP cases remained relatively constant (Graph 5, 6). The slight increase observed among CLP cases was due to an increase in non-isolated in relation to isolated CLP cases.

Graph 4. Annual prevalence of all, isolated and non-isolated cases of cleft lip (CL) in Canada , 1989-2000.

Graph 5. Annual prevalence of all, isolated and non-isolated cases of cleft lip and palate (CLP) in Canada , 1989-2000.

Graph 6. Annual prevalence of all, isolated and non-isolated cases of cleft palate (CP) in Canada , 1989-2000.

Table 2 shows the distribution of clefting cases by sex between 1989 and 2000. Overall, oral clefts were more predominant among males as they represented 58% of all cases. CL and CLP cases were more common in males. Males accounted for 65% of CL (prevalence: 2.2, sex ratio: 0.5) and CLP cases (prevalence: 4.7, sex ratio: 0.5). On the other hand, CP was predominant among females as they accounted for 54% (prevalence: 3.8, sex ratio: 1.2) of CP cases.

Anomaly	Cases	%	Prev*	Ratio ‍†
All clefts
Female	3,308	42.4	7.5	0.7
Male	4,493	57.6	10.2
Cleft lip
Female	518	34.5	1.2	0.5
Male	983	65.5	2.2
Cleft lip and palate
Female	1,116	34.9	2.5	0.5
Male	2,078	65.1	4.7
Cleft palate
Female	1,674	53.9	3.8	1.2
Male	1,432	46.1	3.3

Graphs 7, 8 and 9 show the annual distribution of oral cleft prevalence by sex and by clefting group over the study period. From the year 1991 and onwards, a decreasing pattern in the prevalence of CL among males was observed compared to that of females (Graph 7). This was more evident in the years 1991-1993 and 1995-1997. Despite an increase of CP cases among females in 1997 and 1999, the prevalence of CLP and CP in males and females remained relatively constant during this period (Graphs 8 and 9).

 Graph 7. Annual prevalence of cleft lip (CL) cases by sex in Canada , 1989-2000.

Graph 8. Annual prevalence of cleft lip and palate (CLP) cases by sex in Canada , 1989-2000.

Graph 9. Annual prevalence of cleft palate (CP) cases by sex in Canada , 1989-2000.

Discussion

The prevalence of oral clefting between 1989 and 2000 in Canada was 18.5 per 10,000 births. Most cases during this period were isolated clefts. As for the clefting type, CLP and CP accounted for the vast majority of oral clefts. The proportion of isolated clefts compared with non-isolated clefts was higher among CL and CLP cases and similar among CP cases. There was a decreasing pattern in the prevalence of all CL cases during the study period, particularly in the 1991-1994 and 1996-1999 periods, whereas the prevalence of CLP and CP remained relatively constant.

Overall, oral clefts were more predominant in males. Among CL and CLP cases, males accounted for about two thirds. On the other hand, CP was more common among females. These findings represent closely the distribution of oral clefting by sex among live births and stillbirths in Canada as only <5% of all cases for whom sex data was missing were excluded from the analysis.

Over the 1989-2000 period, a decreasing pattern in the prevalence of CL was observed among males compared to that of females. This was more evident in the years 1991-1993 and 1995-1997. The prevalence of CLP and CP in both males and females remained relatively constant. The decreasing pattern of CL prevalence in males may explain the observed decreasing pattern in the prevalence of CL cases during this period.

The results from this analysis represent nearly all live and still births in Canada between 1989 and 2000. Although data from Nova Scotia before 1996 were not included, this could not have had a significant influence on the results assuming that the ocurrence of clefting in this province does not differ substantially from the rest of the country.

An important limitation is that CCASS does not capture spontaneous abortions neither elective or therapeutic terminations. The analysis, based on live and stillbirths, showed that most oral clefts ocurred without concurrent congenital anomalies. However, since spontaneous abortions and therapeutic terminations are often associated with congenital anomalies, which may include non-isolated oral clefts, the findings may underestimate the true ocurrence of clefting following conception. This is particularly true if oral clefts are common among complex cases with multiple anomalies as those cases are more likely to be diagnosed and terminated. Congenital anomalies data from elective terminations would also be most useful to better assess the extent of such underestimation.

Other important factor that could influence the validity of the results relates to coding practices, which may vary between and within provincial/territorial jurisdictions. Contrary to isolated oral clefts, syndromic clefts that occur in association with other major congenital anomalies may represent challenges for coding interpretation. If only the syndrome is coded rather than its individual anomalies, such as oral clefting, then their ocurrence would be underrepresented. This would be more problematic among CP cases where the proportion of clefts associated with other congenital anomalies, either as part of a syndrome or not, is higher compared to CL and CLP cases. Despite the limitations, the results of this study can be considered as presenting reasonable prevalence values of oral clefting in Canada from 1989 to 2000.

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