Oral Clefts in Saskatchewan : Birth Prevalence Trends Over A Ten-year Period (1994-2003)

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Submitted by Brandy Winquist, William Osei and Ross Findlater, Saskatchewan Health.

I Congenital Anomalies Surveillance in Saskatchewan

 Saskatchewan Health conducts surveillance on a number of important health conditions, including congenital anomalies. While a formal congenital anomaly surveillance system is not in place, limited analyses have been done on congenital anomalies using Saskatchewan Health’s databases. A number of interested agencies have been discussing the development of a formal surveillance system in Saskatchewan.

II Estimating Oral Clefts in Saskatchewan

(i) Methods:

Using hospital separations and birth registry data from 1994-2003, we calculated the live birth prevalence of oral clefts by year and reported trends over the ten-year period. Oral cleft cases were identified from the International Classification of Disease, ICD-9 and ICD–10-CA codes, which included 749.1 or Q36 for cleft lip, 749.2 or Q37 for cleft lip and palate, and 749.0 or Q35 for cleft palate. In Saskatchewan, the ICD-10-CA was implemented in April 2002. Oral cleft cases were included where hospital separation records identified a diagnosis of any oral cleft during the first year of life. Terminated pregnancies and stillbirths were not included. Rates were calculated by sex and for Registered Indian and non-Registered Indian populations. Registered Indians are individuals who are so identified under the Indian Act in Section 6.

(ii) Results:

For the period 1994-2003, the average annual rates for cleft lip (CL), cleft lip and cleft palate (CL/CP), and cleft palate (CP) were 0.28, 0.95, and 0.59 cases per 1,000 live births respectively. Cleft lip rates have remained relatively stable over the ten-year period (see Figure 1). Rates of CL/CP fluctuated from year to year. While CP rates were stable up until the year 2000, there was a notable increase in 2001 and onward.

Table 1: Birth Prevalence By Type of Cleft (<1 year) in Saskatchewan, 1994-2003

Year	Cases of Cleft Lip	Cleft Lip Birth Prevalence Rate (cases/1,000 live births)	Cases Cleft Lip With Cleft Palate	Cleft Lip With Cleft Palate Birth Prevalence Rate (cases/1,000 live births)	Cases Cleft Palate	Cleft Palate Birth Prevalence Rate (cases/1,000 live births)	Live Births*
1994	1	0.07	9	0.64	7	0.50	14,038
1995	5	0.37	17	1.26	4	0.30	13,499
1996	8	0.60	11	0.83	4	0.30	13,300
1997	4	0.31	8	0.62	5	0.39	12,860
1998	3	0.24	13	1.02	4	0.31	12,777
1999	1	0.08	10	0.79	6	0.48	12,604
2000	2	0.17	14	1.15	6	0.49	12,140
2001	3	0.24	16	1.30	12	0.98	12,275
2002	5	0.43	9	0.77	12	1.02	11,761
2003	4	0.33	14	1.16	15	1.25	12,038
Total	36	0.28	121	0.95	75	0.59	127,292

* Total live births, source: Saskatchewan Vital Statistics Annual Reports.

Figure 1: Birth Prevalence (< 1 year) Rate By Type of Cleft, Saskatchewan, 1994-2003

Isolated and Non-isolated Oral Clefts

 For the purpose of this analysis, non-isolated oral clefts are defined as those cases where an oral facial cleft is present in association with one or more congenital anomalies, whether major or minor. Of the 266 cases of oral clefts detected between 1994 and 2003, 76 (28.6%) infants were identified as having non-isolated oral clefts.

Saskatchewan ’s data (refer to Table 2) indicates that infants with CP (35.2%) were more likely to have another anomaly than either those with CL (21.4%) or those with combined CL/CP (26.5%). These findings are consistent with research that has found infants with CP are more likely to also have an associated anomaly than infants with CL or CL/CP (2). At the population level, isolated CL/CP was the most common of the groupings (0.79 per 1,000 live births), whereas non-isolated CL was the least common (0.07 per 1,000 live births).

Table 2: Cases of Cleft Lip, Cleft Palate, Cleft Lip/ Cleft Palate By Isolated and Non-isolated Occurrence*

	Cleft Lip (Prevalence rate/1,000 live births)	Cleft Lip With Cleft Palate (Prevalence rate/1,000 live births)	Cleft Palate (Prevalence rate/1,000 live births)	Total (% of oral cleft cases)
Isolated	33 (0.26)	100 (0.79)	57 (0.45)	190 (28.6)
Non-isolated	9 (0.07)	36 (0.28)	31 (0.24)	76 (71.4)

*denominator, total live births (1994-2003)

Oral Clefts in Males and Females

In the case of cleft lip with or without cleft palate, males are affected more frequently than females with a 2:1 ratio (1). In Saskatchewan, the male-to-female ratio for CL was 2.8:1. Cleft lip with palate was also found more often in males (1.96:1). Over the ten-year period, the number of CP cases was similar for both males and females (1.2:1), although the sex ratio varied considerably by year (data not shown). The relationship is more complex for CP, with complete clefts of hard and soft palate being more common in females and clefts of only soft palate being equally distributed (1). Our analysis did not differentiate between the types of CP, which might explain equal numbers of CP for males and females.

Figure 2: Proportion of Oral Clefts Cases By Sex

Oral Clefts in Registered Indians

Saskatchewan Health data is able to identify the Registered Indian (RI) population in Saskatchewan and use these results to compare the occurrence of oral clefts in RI to rest of the population. Overall, birth prevalence rates of oral clefts are higher in the RI population (refer to Figure 3 and Table 3). Taking a closer look at the data, the birth prevalence of CL was remarkably similar, but the RI population had higher rates of CP and much higher rates of CL/CP (see Table 4). These findings are partly consistent with research in British Columbia that found rates of CL/CP to be higher in RI, although the size of the differences between RI infants and the rest of the population was found to be larger in our analysis (4-5). While our analysis found no difference in CL rates between ethnic groups, studies often collapse cleft lip with or without cleft palate into one group, thereby preventing this type of comparison. Our finding that CP varies notably by ethnic group is contrary to the notion that prevalence is similar across all ethnic groups (1).

A closer look at the data found that the proportions of non-isolated and isolated cases were similar for Registered Indian and non-Registered Indians. Overall, 30% of oral clefts in the Registered Indian population and 28% in non-Registered Indian population occurred in association with another anomaly.

Figure 3: Birth Prevalence Rates of Oral Clefts By Registered Indian and Non-Registered Indian Populations*

Table 3: Oral Clefts By Birth Year, 1994-2002, Registered Indian Status vs. Other Population*

	Registered Indian		Other Population
Year	Number of Cases	Rate Per 1,000 Live Births	Number of Cases	Rate Per 1,000 Live Births
1994	8	3.11	9	0.78
1995	11	4.52	15	1.36
1996	8	3.39	15	1.37
1997	3	1.38	14	1.31
1998	8	4.02	12	1.11
1999	7	2.89	10	0.98
2000	9	3.66	13	1.34
2001	8	3.20	23	2.35
2002	11	4.98	15	1.57

* Data shown here are for the years 1994 through 2002.

Table 4: Types of Oral Clefts By Registered Indian Status, 1994-2002*

	Cases Cleft Lip  (Prevalence Rate Per 1,000 Live Births)	Cases of Cleft Lip With Cleft Palate (Rate Per 1,000 Live Births)	Cases Cleft Palate (Rate Per 1,000 Live Births)	Prevalence Rate of Oral Clefts (CL, CP, CL/P) Per 1,000 Live Births	Live Birth Population (1994-2002)
RI	6 (0.28)	51 (2.41)	16 (0.76)	34.6	21125
Non-RI	26 (0.28)	56 (0.59)	44 (0.47)	13.4	94129

* Data shown here are for the years 1994 through 2002.

III Limitations

There are several limitations to the current analyses. By using hospital separations data, less severe cases of CP missed at birth and diagnosed at outpatient clinics will not have been detected.In addition,changes made to the coding of hospital diagnoses in Saskatchewan likely increased the number of oral cleft cases documented in the health databases from 1999/2000 onward. Prior to 1999/2000, Saskatchewan’s hospital data included up to three main diagnostic fields. In 1999 to 2001, a total of 16 fields became available for each hospital separation, and up to 25 fields in 2001/2002 and beyond when ICD-10-CA was introduced.

Another limitation was that data identifying congenital anomalies in terminated pregnancies or stillbirths is not readily accessible, therefore only live births were included in the current analyses. As a result, cases of oral clefts that occurred in terminated pregnancies or stillbirths would not be detected and the overall number of cases underestimated. Finally, people of aboriginal ancestry who are not registered, including Métis and Inuit people, were included in the non-Registered Indian population.

IV Summary

For the period 1994-2003, the average annual rates for CL, CP, and CL/CP were respectively 0.28, 0.59, 0.95 cases per 1,000 live births. Almost one-third of infants were identified as having oral clefts in association with another anomaly . Male infants were more commonly affected by CL and CL/CP than females, while rates of CP were similar for both sexes. Cleft palate and CL/CP both had higher rates in the Registered Indian population, but CL rates did not differ across ethnic groups.

While CP rates have increased since 1999/2000, it may be that this is an artifact due to coding changes rather than a true increase. By allowing for more diagnostic codes, the new coding practices have probably led to elevated rates of CP through improved documentation. However, it is interesting to note that the increase is not as notable for CL or CL/CP. Future surveillance tracking this increase will be necessary.

References:

1. Health Canada. Congenital anomalies in Canada -- a perinatal health report, 2002. Ottawa: Minister of Public Works and Government Services Canada, 2002. Available at: http://www.phac-aspc.gc.ca/publicat/cac-acc02/pdf/cac2002_e.pdf
2. March of Dimes. Cleft lip and cleft palate. Available at: http://www.marchofdimes.com/professionals/14332_1210.asp
3. Jones KL. Smith’s Recognizable Patterns of Human Malformation, 4 th edition. Toronto: W.B. Saunders Company, 1988: 10-2.
4. Lowry RB, Thunem NY, Silver M. Congenital anomalies in American Indians of British Columbia. Genetic Epidemiology;3(6):455-67, 1986.
5. Lowry RB, Trimble BK. Incidence rates for cleft lip and palate in British Columbia 1952-71 for North American Indian, Japanese, Chinese and total populations: secular trends over twenty years. Teratology 1977;3:277-83.

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