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Trends & Clusters

CARIS doesn’t have its own surveillance programme but collaborates with EUROCAT so that Welsh data can be checked for any long term trends or clusters.

EUROCAT have developed a sophisticated statistical programme to analyse data for trends and cluster over time. Data sent by CARIS is checked annually and the results fed back to the register.

Data from CARIS is also combined with the other European registers to look for wider changes in trends across Europe.

Surveillance of Congenital Anomalies

CARIS has limited resources to carry out its own detailed surveillance of congenital anomalies. Membership of the European network of congenital anomaly registers (EUROCAT) and the International Clearing House of Birth Defect Registers Surveillance and Research (ICBDSR) provides two mechanisms for routine surveillance to be carried out on Welsh data.


EUROCAT performs annual statistical monitoring for both trends and clusters in time in order to detect signals of new or increasing teratogenic exposures which may require public health action.  This relates to two of EUROCAT’s objectives:

  • to provide essential epidemiologic information on congenital anomalies in Europe

  • to co-ordinate the detection of, and response, to clusters and early warning of teratogenic exposures

Statistical monitoring is essentially a screening method to scrutinise data regularly and systematically to detect any previously unrecognised increases in frequency of congenital anomalies which may be associated with exposure to teratogenic drugs or environmental chemical pollutants.  It aims to identify potential cause for concern where there is no specific prior hypothesis about the exposure.

An annual Statistical Monitoring Report is published detailing the cluster and trends detected by statistical monitoring conducted at EUROCAT Central Registry and the methodology used. The annual report also includes the results of the preliminary investigations into the identified clusters and trends carried out by local registries. 

Member registries are invited to use the EUROCAT Data Management System (DMS) locally for cluster detection and report their results to Central Registry.

The elements of the current monitoring strategy are:

  • Common user-friendly statistical software for use centrally and locally (DMS)

  • Annual statistical monitoring for trends and clusters at central level, 15 months after last date of birth (e.g. year 2020 births included in monitoring in March 2021).

  • More frequent and/or earlier statistical monitoring locally (by member registries)

  • Use of EUROCAT communications and special data analyses to respond to news about clusters identified locally or outside the monitoring system

  • A clear and prompt system of investigation and reporting of results

  • Use of statistical monitoring additionally as a data quality control system

Trend tests are performed for 81 anomaly subgroups for each registry. Currently, Central Registry performs a trend test for the most recent five years of data, as well as a trend test for the most recent 10 years (or 8 years if 10 years are not available).

The analysis is based on the number of cases per year of birth and the number of births per year. Data is presented by individual year or grouped by two year intervals if there are too few cases to meet the criterion for testing by single year. 

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