Abdominal defects

Recent reports from England and Wales[1] and Scotland[2] imply that a gradient of increasing risk of congenital abdominal wall defects may exist from the south to the north of the United Kingdom. We tested this hypothesis by comparing data from a validated public health surveillance system in the west of Scotland with other registers in the United Kingdom.[3 4]

Subjects, methods, and results

The Glasgow Register of Congenital Anomalies is a computerised epidemiological database run by the Greater Glasgow Health Board since 1974. A member of the transnational network of EUROCAT (European Registration of Congenital Anomalies) since 1980, it uses multiple sources of ascertainment and subjects all notified anomalies to systematic diagnostic validation. Completed registration forms are transmitted electronically to the EUROCAT central registry in Brussels, where they are checked for completeness and accuracy of coding[3] There is no formal time limit for notification. All births and induced abortions following prenatal diagnosis are included in the surveillance. Diagnostic coding is based on the British Paediatric Association's extension to the ninth revision of the International Classification of Diseases.

The numerators were all registered cases of omphalocele (code 75670) and gastroschisis (code 75671) in mothers resident within the area covered by the Greater Glasgow Health Board at the time of delivery; cases were included that occurred in live births, still births, and induced abortions for 1980-93 inclusive. Induced abortions were counted in the year of the expected date of delivery had the pregnancy continued. The denominators were the total births to mothers in the area in the relevant time period. Prevalence was calculated by dividing the numbers for each defect by total births. Prevalences were compared using [Chi-square] tests, and ratios of omphalocele to gastroschisis using a [Chi-square] test for heterogeneity of odds ratios.

During the study there were 73 cases of omphalocele (4.08 per 10 000 births), of which 34 (47%) were induced abortions, and 24 cases of gastroschisis (1.34 per 10 000 births), of which 5 (21%) were induced abortions. The apparently high prevalence of abdominal wall defects in Glasgow relative to other parts of the United Kingdom was due to its exceptionally high rate of omphalocele (table).

(*) Prevalence of all abdominal wall defects ranged from 1.23 per 10 000 births in South West Thames region to 3.11 per 10 000 births in Northern region.

Comment

Our data support the hypothesis of an increasing gradient in the prevalence of congenital anterior abdominal wall defects from the south to the north of the United Kingdom. Whether the phenomenon is real or artefactual (due to varying ascertainment) remains uncertain. In Glasgow the risk of omphalocele seems especially high. The prevalence of omphalocele in our study is about four times higher than that reported by the Office for National Statistics for England and Wales. However, this striking discrepancy may reflect substantial underascertainment by the Office for National Statistics of cases of omphalocele.[4] In particular, these national data excluded terminations of pregnancy following prenatal diagnosis, whereas almost half of the cases in our series were terminated. Data from EUROCAT for 1980-92 indicate that the ratio of omphalocele to gastroschisis was 2.5,[3] a value much closer to that of Glasgow (3.0) than that of the Office for National Statistics (0.8). By contrast, the prevalence of gastroschisis in Glasgow is comparable with that of the area covered by the Office for National Statistics, particularly its northern and western regions.

The reported gradient from south to north in the prevalence of abdominal wall defects (especially omphalocele) in the United Kingdom and in Europe as a whole[5] is similar to that observed for neural tube defects and could reflect a common aetiology. Further work is needed to determine the relative influence of ascertainment, maternal factors (such as age, socioeconomic group, and smoking), and underlying secular trends on these geographical variations.

We thank Mrs Hilary Miller and Dr John Womersley of the department of public health, Greater Glasgow Health Board, for their help and support in collating and analysing data from the Glasgow Register of Congenital Anomalies. The EUROCAT network is supported by the European Commission.

Contributors: DHS initiated the study, helped plan the methods, and participated in the analysis, in interpreting data, and in writing the paper. SR helped to conceive the study, collated the data, and contributed to the analysis and writing the paper as part of a wider project on the epidemiology of abdominal wall defects. WHG contributed to methodological aspects of the study, including the analysis, presentation, and interpretation of the results. DHS is guarantor for the study.

Funding: None.

Conflict of interest: None.

[1] Tan KH, Kilby MD, Whittle MJ, Beattie BR, Booth IW, Botting BJ. Congenital anterior abdominal wall defects in England and Wales 1987-93: retrospective analysis of OPCS data. BMJ 1996;313:903-6.

[2] Chalmers J, Forrest J, Cant B, Hollinsworth M. Congenital anterior abdominal wall defects. BMJ 1997;3314:371-2.

[3] EUROCAT Working Group. Surveillance of congenital anomalies in Europe 1980-1992. Brussels: Institute of Hygiene and Epidemiology, 1995. (EUROCAT report 6.)

[4] Dillon E, Renwick M, Rankin J. Congenital anterior abdominal wall defects. BMJ 1997;314:372.

[5] Calzolari E, Bianchi F, Dolk H, Milan M, EUROCAT Working Group. Omphalocele and gastroschisis in Europe: a survey of 3 million births. Am J Med Genet 1995;58:187-94.

(Accepted 27 March 1998)

DH Stone, director Shahnaz Rimaz, postgraduate student Paediatric Epidemiology and Community Health Unit, Department of Child Health, University of Glasgow Yorkhill, Glasgow G3 8SJ

W H Gilmour, senior lecturer Departments of Statistics and Public Health, University of Glasgow, Glasgow G12 8RZ

Correspondence to: Dr Stone D.H.Stone@clinmed.gla.ac.uk

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