Prevalence and Geographic Disparities in Certain Congenital Anomalies in Quebec: Comparison of Estimation Methods

Robert Choinière, Michel Pageau and Marc Ferland

The purpose of this study was to estimate the prevalence of congenital anomalies in Quebec from MED-ECHO hospitalization records and from records of stillbirths. The results are first compared with those from the Canadian Congenital Anomalies Surveillance System (CCASS) for Quebec and Canada; then the data are examined by period and region of residence. The study results show that, for the congenital anomalies selected for the study, the prevalence rates measured for Quebec from the MED-ECHO data tend to be lower than the prevalence rates for Canada, whereas the rates estimated by CCASS are higher for Quebec than for Canada. The MED-ECHO data cover practically all Quebec births, compared with only 15% coverage by CCASS, and therefore provide a more accurate picture of congenital anomalies in Quebec.

Key words: congenital anomalies; disparities; estimates; evolution; prevalence; Quebec

Background

In its 1992 health and welfare policy, Quebec set itself the goal of reducing the incidence of congenital anomalies. In Quebec, congenital anomalies are the second leading cause of perinatal death and the sixth leading cause, in terms of years of potential life lost, of premature death.¹ Approximately 40% of all babies who die during the first year of life and over 30% of children admitted to a hospital pediatric department have a congenital defect.¹ Furthermore, it has been shown that children born with congenital anomalies are much more likely than others to suffer adverse long-term consequences to their health, quality of life and survival, such as prolonged periods in hospital; multiple surgeries; disrupted physical, intellectual or motor development; and respiratory, visual, auditory or language disorders.^1-3

Since there is no registration or surveillance system for congenital anomalies in Quebec, there is very little accurate, recent information on the overall incidence of the births of children with congenital defects.^1,4 Thus, it is difficult to know whether Quebec's goal of reducing congenital anomalies is being achieved. In Canada, the only source of information on the birth prevalence of congenital anomalies is the Canadian Congenital Anomalies Surveillance System (CCASS), which for several years has been administered through the Laboratory Centre for Disease Control (LCDC), Health Canada.⁵ However, the data are not fully representative of Quebec.

CCASS uses provincial data on cases of congenital defects obtained exclusively from hospital admission/separation records of stillborns, newborns and infants during the first year of life.⁶ CCASS does not include cases associated with medical termination of pregnancy for congenital defects, or with miscarriages and abortions, and this limits the coverage of the prevalence of congenital anomalies.

Since there may be several hospitalizations per individual, CCASS uses a melding process to combine information compiled on a single patient during different hospital stays. This process matches variables such as sex, date of birth, residential postal code and health insurance number.

The portion of Quebec hospitalization records compiled by MED-ECHO (the Quebec hospitalization database) and sent to Health Canada does not contain all the information needed to identify individuals and meld cases.⁵ Therefore, LCDC incorporates into CCASS the Quebec hospitalization data from the Hospital Medical Records Institute (HMRI), an organization that for several years has been administered by the Canadian Institute for Health Information. These data have the advantage of containing the information needed for melding, but the major disadvantage of covering only a small proportion of hospital births in Quebec. From 1989 to 1991, only 15% of Quebec births were captured by the HMRI database,⁵ whereas from 1989 to 1995, 99% of live births were registered by MED-ECHO. The CCASS data for Quebec are therefore incomplete and cannot be used to estimate the number of congenital anomalies or accurately measure prevalence.

The goal of this study was to estimate the prevalence of congenital anomalies in Quebec using MED-ECHO data, which are more complete than the HMRI data used by CCASS. We had access to several variables that are not included in the version of MED-ECHO data sent to Health Canada. This enabled us to use identifiers comparable to the ones available from the HMRI database while covering almost all births in Quebec. By combining these data with those from the records of stillbirths, we therefore expect to obtain more accurate results and statistically more robust rates, because they are based on a larger number of events. A deterministic melding method was selected, which is different from, but comparable to, the probabilistic one used in CCASS.

Methods

Data

To estimate the prevalence of congenital anomalies in Quebec as accurately as possible, we used the congenital defects cases from the MED-ECHO hospitalization database and from stillbirth records, which MED-ECHO does not cover. MED-ECHO is the Quebec database on short-term hospitalizations and day surgeries performed in Quebec. Each record contains identifying, demographic information along with the primary diagnosis on admission and 15 possible secondary diagnoses.^4,7 As in the case of CCASS, it was not possible to include cases associated with medical terminations of pregnancy for congenital defects, or with miscarriages and abortions.

The data relating to an individual can be melded using the probabilistic or the deterministic method, depending on the quantity and quality of the information available for correctly identifying individuals.⁸ When little information is available, as is the case for CCASS, a probabilistic approach is recommended (based, as its name suggests, on probabilities). To build its database, CCASS uses a variation of this method that involves ad hoc weighting based on a system of weighting factors.⁹

When a large amount of high-quality data is available, a deterministic approach that makes links according to criteria established by the researchers is often preferable. The deterministic method has the advantage of being easier to apply while producing better results than the probabilistic approach.¹⁰ For these reasons, we chose the deterministic approach for this study.

The variables that CCASS selects from MED-ECHO to meld hospitalizations are sex, date of birth, six-digit postal code, health insurance number and the codes from the Ninth Revision of the International Classification of Diseases (ICD-9) for the main diagnosis and the 15 secondary diagnoses. To maximize melds, the following variables were added to these identifiers: admission date, discharge date, medical record number, hospital code, municipality code, regional county municipality code (MRC), local community services centre code (CLSC), type of death, type of care, civil status, origin code and destination code.

Using a deterministic melding procedure, we estimated the number of infants who were hospitalized for congenital anomalies at least once during their first year of life by regrouping the different hospitalization records for each child under the age of one. This was done for the fiscal years from 1988/89 to 1996/97.

The first step consisted of matching hospitalizations by file number, because only one file number can be assigned to an individual in the same hospital no matter how many visits are made. In the second step, hospitalizations with identical health insurance numbers were matched, as these represent another identifier unique to every individual. However, health insurance numbers are frequently available only several months after the child's birth and therefore cannot be used to link visits occurring in the first few months of life. Finally, in the later stages, the following four remaining matches were made based on the place of residence of the hospitalized individuals.

• Identical postal code (six digits), date of birth and sex
• Identical municipality code, CLSC code, date of birth and sex
• Identical postal code (three digits), CLSC code, date of birth and sex
• Identical postal code (three digits), municipality code, date of birth and sex

For the last four melding procedures to be acceptable, each match had to meet the following conditions: the civil status for a second visit could not be "newborn," the discharge from a first visit could not be due to death, the admission date for a second visit could not precede by more than one day the discharge date of the preceding visit and, if the admissions were to the same hospital, the file numbers could not be different.

For matches based on the file number and the health insurance number where the date of birth varied between the two visits, we assumed that the date on the first visit was the most accurate. When the sex varied from one visit to another, we used the sex from the most recent visit.

The final operation needed to create the congenital abnormalities database for Quebec was to remove certain cases of contradictory diagnoses using information previously provided by CCASS. Some cases initially identified as congenital anomalies were also associated with particular diagnoses that cancelled the initial diagnosis. Finding one of these diagnoses in addition to a diagnosis of congenital anomalies for the same hospitalization implied there was a contradiction among diagnoses and that this hospitalization, according to CCASS, should not be included among the congenital anomalies.

Table 1 summarizes the procedures carried out on all hospitalizations for congenital anomalies in the MED-ECHO database involving newborns and infants under the age of one.

The data on stillbirths were taken from the stillbirths database for the calendar years 1989-1996. No melding is needed for stillbirths because the cases are unique.

Prevalence and Comparisons

Once we had finished melding the Quebec data on congenital anomalies, we estimated the prevalence of particular congenital anomalies and compared our results with the CCASS results for Canada and Quebec. We also used our Quebec data to examine changes over time and, for certain congenital anomalies, the disparities among health and social services regions.

Like the LCDC researchers, we selected 14 major, relatively common and fairly easily diagnosed congenital anomalies in order to compare our data with the CCASS data⁵ (Table 2).

The Quebec rates were calculated for the period 1989-1991 for each of the anomalies and compared with the CCASS rates for the same period.⁵ We also compared the rates for the 1989-1991 period with those for 1993-1995. Finally, for the 10 most common anomalies among the 14 selected, we examined regional disparities during 1989-1995.

Results

During 1989-1991, the CCASS data showed that Quebec recorded prevalences significantly higher than the Canadian average for 9 out of 14 anomalies (Table 3). However, the results were obtained from data covering only 15% of births throughout Quebec and therefore were not necessarily representative of the Quebec situation. In the 1995 Status Report on CCASS, the authors explained this data limitation: "Since hospitals report to HMRI on an individual basis, hospitals that choose to participate may be more specialized and receive more readmissions of infants with congenital anomalies. This will result in higher provincial rates being reported."⁵

TABLE 3 Prevalence rates (per 10,000 total births) of particular congenital anomalies (in infants <1 year old) by data source, 1989-1991, Quebec and Canada
		Data source
ICD-9 code	Congenital anomaly	MED-ECHO and stillbirths database: Quebec			CCASS:5 Quebec			CCASS:5 Canada
740.0-740.2	Anencephalus and similar anomalies	*	1.1	(-)	**	1.4		2.4
741.0-741.9	Spina bifida		6.8			9.9		7.8
742.0	Encephalocele	*	1.0	(-)	**	1.6		1.5
742.3	Congenital hydrocephalus		6.8			14.6	(+)	7.7
745.1	Transposition of great vessels		4.9			15.3	(+)	4.8
746.7	Hypoplastic left heart syndrome		2.6	(-)	*	8.0	(+)	3.4
749.0	Cleft palate		6.9			11.8	(+)	7.3
749.2	Cleft palate with cleft lip		4.9	(-)	*	7.8		8.2
750.3	Tracheo-esophageal fistula, esophageal atresia and stenosis		3.4		*	8.5	(+)	3.8
751.2	Atresia and stenosis of large intestine, rectum and anal canal		5.4			13.4	(+)	5.8
753.0	Renal agenesis and dysgenesis		5.2		*	7.5	(+)	5.0
755.2-755.4	Reduction of limb		5.3		*	5.2		4.6
756.7	Anomalies of abdominal wall		4.5		*	7.3	(+)	4.7
758.0	Down's syndrome		12.4	(-)		24.9	(+)	14.3
*Coefficient of variation greater than 16.5% and less than or equal to 33.3%. The value should be interpreted with caution. **Coefficient of variation greater than 33.3%. The value is shown as an indication only. (+)/ (-)Rate significantly higher or lower than the Canadian rate (p <= 0.05)

TABLE 4 Number of cases and prevalence rates (per 10,000 total births) of particular congenital anomalies (in infants <1 year old), 1989-1991 and 1993-1995, Quebec
ICD-9 code	Congenital anomaly	Number of cases: 1989-1991	Number of cases: 1993-1995	Rates: 1989-1991	Rates: 1993-1995	Variation from 1989-1991 to 1993-1995
740.0-740.2	Anencephalus and similar anomalies	40	23	* 1.1	* 0.9
741.0-741.9	Spina bifida	194	147	6.8	5.5
742.0	Encephalocele	28	32	* 1.0	* 1.2
742.3	Congenital hydrocephalus	193	183	6.8	6.9
745.1	Transpositon of great vessels	140	139	4.9	5.2
746.7	Hypoplastic left heart syndrome	75	73	2.6	2.7
749.0	Cleft palate	195	195	6.9	7.3
749.2	Cleft palate with cleft lip	140	148	4.9	5.6
750.3	Tracheo-esophageal fistula, esophageal atresia and stenosis	97	91	3.4	3.4
751.2	Atresia and stenosis of large intestine, rectum and anal canal	153	137	5.4	5.1
753.0	Renal agenesis and dysgenesis	148	164	5.2	6.2
755.2-755.4	Reduction of limb	150	124	5.3	4.7
756.7	Anomalies of abdominal wall	127	171	4.5	6.4
758.0	Down's syndrome	353	332	12.4	12.5
* Coefficient of variation greater than 16.5% and less than or equal to 33.3%. The value should be interpreted with caution. () / ()Significant reduction or increase between the two periods (p<= 0.05)

Discussion

The CCASS data for Quebec are taken from the records of the HMRI, which covers only a small proportion of Quebec births and therefore cannot be used to accurately estimate the prevalence of congenital anomalies in Quebec.⁵

This study shows that using hospitalization data from MED-ECHO could be a worthwhile solution for CCASS. The MED-ECHO database covers virtually all Quebec births and contains the necessary information for melding the various hospitalizations for one individual.

The study makes it possible for the first time to accurately estimate the prevalence of particular congenital anomalies in Quebec and follow them over time. It also enables regional comparisons to be made and Quebec rates to be compared with overall rates in Canada.

The results show that, for the selected anomalies, the prevalence rates tend to be lower in Quebec than in Canada and there is little variation over time. Because of the strong variability of the data measured by region, regional comparisons do not yield clear trends.

To obtain even more accurate data on congenital anomalies, it will be necessary to include the information on medical termination of pregnancy for congenital anomalies, and on miscarriages and abortions, as has been done in international systems.^4,11,12 Such additions are especially worthwhile given the improvement and greater availability of early detection methods (ultrasonography, cord puncture, amniocentesis, trophoblast biopsy, etc.).^13,14

Although the deterministic approach is superior to the probabilistic approach for linking the various events relating to one individual, using a single identifier to follow one person among all the data sources is by far the most accurate method of measuring the actual number of congenital anomalies.^8,10

The role played by administrative practices in relation to hospitalization should be measured in geographic and temporal comparisons of the prevalence of congenital anomalies. It is possible that higher levels of congenital anomalies simply reflect a greater propensity to indicate a congenital anomaly code.

Finally, it remains to be seen which of the anomalies could be selected as sentinel causes.

Acknowledgements

This study received financial support from the Bureau of Reproductive and Child Health of the Laboratory Centre for Disease Control. The authors would like to thank Jocelyn Rouleau of that Bureau.

References

1. Ministère de la Santé et des Services sociaux. Politique de périnatalité. Quebec: Government of Quebec, 1993:21-2.

2. Ministère de la Santé et des Services sociaux. La politique de la santé et du bien-être. Quebec: Government of Quebec, 1992:66-71.

3. Soltani MS, Guediche MN, Bchir A, Ghanem H, Pousse H, Braham A. Facteurs associés aux faibles poids de naissance dans le Sahel tunisien. Archives françaises pédiatriques 1991;48:405-8.

4. De Wals P, Royer-Trochet C. Évaluation des bases de données sanitaires pour la recherche et la surveillance épidémiologique des malformations congénitales. Régie régionale de la santé et des services sociaux de la Montérégie, 1997.

5. Rouleau J, Arbuckle TE, Johnson KC, Sherman JG.Description and limitations of the Canadian Congenital Anomalies Surveillance System (CCASS) [status report]. Chronic Dis Can 1995;16(1):37-42.

6. Johnson KC, Rouleau J. Temporal trends in Canadian birth defects birth prevalences, 1979-1993. Can J Public Health 1997;88(3):169-76.

7. Ministère de la Santé et des Services sociaux. Les banques de données du MSSS. Numéro 1. Données sur la clientèle hospitalière (MED-ÉCHO). Quebec: MSSS, 1986.

8. Turner D, Roos LL, Traverse D, Stranc L, Harrison M, Fields ALA, Bryant H. Forging partnerships through data: a general strategy for record linkage. In: Information technology in community health. Victoria: School of Health Information Science, University of Victoria; 1998:1-2-1-6.

9. Canadian Congenital Anomalies Surveillance System. Melding process description [working document]. Ottawa: Laboratory Centre for Disease Control, 1997.

10. Roos LL, Wajda A. Record linkage strategies. Part I: estimating information and evaluating approaches. Methods of Information in Medicine 1991;30:117-23.

11. EUROCAT. 15 years of surveillance of congenital anomalies in Europe 1980-1994.Brussels: Scientific Institute of Public Health - Louis Pasteur, 1997.

12. International Clearinghouse for Birth Defects Monitoring Systems. Congenital malformations worldwide. Amsterdam, 1991.

13. Gérard CH, Gillerot Y, Koulischer L, Hustin J. Amniocentèse et biopsie trophoblastique. Journal gynécologique-obstétrique-biologique et reproductif de Paris 1991;20:617-22.

14. Gougard J, Ayme S, Stoll CL. L'évaluation des technologies diagnostiques des malformations congénitales. Journal gynécologique-obstétrique-biologique et reproductif de Paris 1992;21(3):278-80.

Robert Choinière, Régie régionale de la santé et des services sociaux (RRSSS) de Montréal-Centre, Direction de la santé publique, 3725, rue Saint-Denis, Montréal (Québec) H2X 3L9; Fax: (514) 286-5782; E-mail: Robert_Choinière@ssss.gouv.qc.ca

[Table of Contents] [Next]