International Journal of Epidemiology, Vol 28, 258-262, Copyright © 1999 by International Epidemiological Association
J Reefhuis, HE de Walle and MC Cornel
BACKGROUND: While monitoring birth defects in a registry, statistically
significant increases in prevalence occasionally occur. In the European
Registration Of Congenital Anomalies (EUROCAT) in the Northern Netherlands
20000 births are monitored every year. For omphaloceles, a steady increase
in the prevalence from 0.86 per 10000 live- and stillbirths in 1981-1983 to
3.11 per 10000 live- and stillbirths in 1994 was seen in the three northern
provinces of The Netherlands. METHODS: A stepwise enquiry into this
increase, which included checking for misclassification and change in
coding and ascertainment when necessary, was done. All cases of omphalocele
and associated or similar birth defects registered at the EUROCAT registry
were retrieved and if necessary recoded. RESULTS: This study showed that
the increase reported previously was not a true time trend. A few cases of
e.g. diastasis recti and trisomy 18 were misclassified. The prevalence in
more recent years is comparable with that in the rest of Europe, whereas it
used to be lower. There was an increase in isolated omphalocele, but the
numbers are small. CONCLUSIONS: The stepwise enquiry described should be a
standard procedure after noticing an increasing prevalence in a registry. A
better subdivision, e.g. in isolated cases versus children with multiple
congenital anomalies, before monitoring can contribute to a lower number of
false positive signals.
ARTICLES
Artefactual increasing frequency of omphaloceles in the Northern Netherlands: lessons for systematic analysis of apparent epidemics
Department of Medical Genetics, University of Groningen, The Netherlands.
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