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Linking maternity data for Wales, 2005-07: methods and data quality

Datta-Nemdharry, P., Dattani, N. & Macfarlane, A. J. (2012). Linking maternity data for Wales, 2005-07: methods and data quality. Health Statistics Quarterly, 54, pp. 1-24.


Background: This work formed part of a project to link data recorded routinely at birth in England and Wales to bring together socio-demographic data and data about care at birth. Birth registration data for England and Wales had already been linked to the National Health Service (NHS) Numbers for Babies’ data (NN4B) recorded when an NHS number is issued to a new baby. The data for babies born between 2005 and 2007 to mothers resident in England were then further linked to their records in the Maternity Hospital Episode Statistics (HES). This paper describes the linkage of linked birth registration and NN4B records for babies of mothers resident in Wales for 2005 to 2007 to the Patient Episode Database for Wales (PEDW) and the National Community Child Health Database (NCCHD) records.

Methods: Birth registration and NN4B records were first linked to NCCHD records, which contains data about the children born. This dataset was further linked to PEDW to obtain maternity records relating to their delivery. The linkage was carried out using pre-defined linkage algorithms. The quality of the Welsh data was assessed in terms of completeness of data and concordance of common data items in relation to birth registration wherever possible. NN4B data were used for data items not collected at birth registration, such as gestational age for live births.

Results: Around 92 per cent of registration/NN4B records for the three years could be linked to NCCHD and PEDW records. Different data fields were provided from each of the two Welsh data sources, with the common and key data items, such as birth weight and gestational age, coming from NCCHD.
Overall the percentage of missing data in NCCHD was minimal, with the exception of ethnicity which was missing from 13 per cent of records in NCCHD in 2005 but from fewer records in subsequent years. For births in 2005 and 2006, over 30 per cent of NN4B records linked to registration did not have the mother’s NHS number compared with less than 1.1 per cent of NCCHD records. There was excellent agreement between the data items in linked birth registration and NN4B files and the data from NCCHD with over 95 per cent concordance in common data items. Around 99 per cent of the linked records had the same ethnic group which is not surprising as records on the child health system databases and NN4B are derived from a common data source.

Conclusion: The linkage rate for maternity data in Wales was similar to that obtained in linking registration/NN4B linked data to the Maternity HES records for England but the data were of higher quality and were more complete. Therefore, NCCHD linked to PEDW could be used to analyse birth outcomes for Wales without the need to link to birth registration and NN4B data. Nevertheless data items such as mother’s country of birth and socio-economic status are recorded only at birth registration so linkage to the birth registration/NN4B dataset can generate a much fuller set of data items and enable analyses of birth outcomes by factors such as ethnicity, socio-economic status and parents’ country of birth.

Publication Type: Article
Additional Information: © 2012 Crown Copyright. This paper is covered by the Open Government Licence for public sector information
Subjects: H Social Sciences > HA Statistics
R Medicine > RA Public aspects of medicine
Departments: School of Health & Psychological Sciences > Midwifery & Radiography
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