BMJ  2005;330:27 (1 January), doi:10.1136/bmj.38300.665301.3A (published 23 November 2004)

Information in practice

Congenital anomaly surveillance in England—ascertainment deficiencies in the national system

¹ National Perinatal Epidemiology Unit, University of Oxford, Oxford OX3 7LF, ² London School of Hygiene and Tropical Medicine, London WC1E 7HT, ³ Faculty of Life and Health Sciences, University of Ulster, Newtonabbey, Co Antrim, BT37 0QB, ⁴ Office for National Statistics, London SW1V 2QQ, ⁵ North Thames Perinatal Public Health Unit, Northwick Park Hospital, Harrow, HA1 3UJ, ⁶ School of Population and Health Sciences, Faculty of Medicine, University of Newcastle, Newcastle NE2 4HH, ⁷ International Agency for Research on Cancer, 150, Cours Albert Thomas, 69372 Lyons, Cedex 08, France, ⁸ Wessex Clinical Genetics Service, Princess Anne Hospital, Southampton SO16 5YA

Abstract

Objective Firstly, to assess the completeness of ascertainment in the National Congenital Anomaly System (NCAS), the basis for congenital anomaly surveillance in England and Wales, and its variation by defect, geographical area, and socioeconomic deprivation. Secondly, to assess the impact of the lack of data on pregnancies terminated because of fetal anomaly.

Design Comparison of the NCAS with four local congenital anomaly registers in England.

Setting Four regions in England covering some 109 000 annual births.

Participants Cases of congenital anomalies registered in the NCAS (live births and stillbirths) and independently registered in the four local registers (live births, stillbirths, fetal losses from 20 weeks' gestation, and pregnancies terminated after prenatal diagnosis of fetal anomaly).

Main outcome measure The ratio of cases identified by the national register to those in local registry files, calculated for different specified anomalies, for whole registry areas, and for hospital catchment areas within registry boundaries.

Results Ascertainment by the NCAS (compared with data from local registers, from which terminations of pregnancy were removed) was 40% (34% for chromosomal anomalies and 42% for non-chromosomal anomalies) and varied markedly by defect, by local register, and by hospital catchment area, but not by area deprivation. When terminations of pregnancy were included in the register data, ascertainment by NCAS was 27% (19% for chromosomal anomalies and 31% for non-chromosomal anomalies), and the geographical variation was of a similar magnitude.

Conclusion The surveillance of congenital anomalies in England is currently inadequate because ascertainment to the national register is low and non-uniform and because no data exist on termination of pregnancy resulting from prenatal diagnosis of fetal anomaly.

Introduction

Monitoring of congenital anomalies is vital for identifying possible clusters and trends and addressing concerns about putative environmental teratogens. A national register for England and Wales, now called the National Congenital Anomaly System (NCAS), was proposed by the minister of health in 1963 after the thalidomide "epidemic." It is run by the Office for National Statistics (ONS; www.statistics.gov.uk).

Notification of anomalies in live and stillbirths to NCAS is voluntary, usually through a standard paper form filled in by midwives, health visitors, and other health professionals. Local congenital anomaly registers have also been set up, partly to deal with the known under-ascertainment^1-4 and partly to meet local and research needs. Some 50% of births in England are covered by local congenital anomaly registers. These registers are all members of the British Isles Network of Congenital Anomaly Registers (BINOCAR; www.statistics.gov.uk.binocar) and the European Network of Congenital Anomaly Registers (EUROCAT; www.eurocat.ulster.ac.uk). In contrast to the NCAS, these local registers record fetuses terminated for fetal anomaly. Ascertainment of cases to the local registers is actively sought and provided from multiple sources, such as cytogenetic and postmortem reports; prenatal diagnosis; and paediatric, neonatal, orthopaedic, and surgical units.

As part of a study of the geographical variation in the prevalence of birth defects⁵ we measured the extent to which the under-ascertainment in the NCAS data compared with four local registers, varied by defect, geographical area, and socioeconomic deprivation. We also assessed the impact of the absence of data on pregnancies terminated because of fetal anomaly from the national data set.

Methods

We used data from four local English congenital anomaly registers for comparison with the NCAS. North Thames (West) Congenital Malformation Register (NTW) covers 45 000 births per year; Northern Congenital Abnormality Survey (NorCAS), 33 000 births per year; Wessex Antenatally Diagnosed Congenital Anomalies Register (WANDA), 25 000 births per year; and Oxford Congenital Anomaly Register (OXCAR), 6000 births per year. The study period was nine years (1991-9) except WANDA, which started in 1994 and contributed cases from 1994 to 1999 inclusive. The four local registers use similar methods, with active case finding and multiple sources of ascertainment. Each register collects information on all congenital anomalies occurring in miscarriages after 20 weeks' gestation, in live births and still births, and in fetuses terminated after prenatal diagnosis of anomaly.

As three of the local registers were not entirely population based, we reduced their populations to those census wards where at least 80% of mothers delivered in hospitals reporting to the register. We extracted cases reported to NCAS for the same wards. We compared total numbers of notified cases from the two sources (NCAS and local registers) by condition. We defined hospital catchment areas as the collection of census wards in which most resident mothers delivered in a particular hospital. We calculated the Carstairs deprivation index for each enumeration district.

We selected for study major defects for which the degree of ascertainment is high, agreement on case definition by all registries is good, and ICD-10 lists specific codes (table).

View this table: [in this window] [in a new window]   Congenital anomalies studied in the National Congenital Anomaly System (NCAS) for England and Wales and four local congenital anomaly registers in England, 1991-9. Values are numbers of cases unless otherwise indicated

 

We calculated the ratio of the number of cases in the NCAS data to the number in the local register data, overall and by anomaly type, region, hospital catchment area, and deprivation group dividing at quintiles. We also used a logistic model to adjust the results for deprivation group (dividing at quintiles) by hospital catchment area and region.⁵ We carried out all analyses twice; the first excluded terminations of pregnancy present in local registers and the second included them.

Results

Ascertainment by NCAS was 40% (42% for non-chromosomal anomalies and 34% for chromosomal anomalies) when terminations of pregnancy were excluded from register data. This varied markedly by register, hospital catchment area, and congenital anomaly subgroup (table); all variations were significant (P < 0.001).

When terminations of pregnancy were included in register data, ascertainment of cases by NCAS was 27% (31% for non-chromosomal anomalies and 19% for chromosomal anomalies) and again varied markedly by register, hospital catchment areas within register areas (fig), and congenital anomaly subgroup; all variations were significant (P < 0.001).

View larger version (47K): [in this window] [in a new window]   Ascertainment ratios to NCAS by hospital catchment area for all cases. (a) Termination of pregnancy is excluded. (b) Termination of pregnancy cases is included. Ascertainment ratios are shown for each hospital catchment, with 95% confidence intervals. Catchments with fewer than 10 anomalies identified by either source were omitted, to avoid distracting imprecise ratios

 

The lowest ascertainment was for neural tube defects (11% when terminations are included in local register data, 68% when excluded) and cardiac defects (12% and 13%), and the highest for cleft lip (75% and 83%) and for limb reduction defects (73% and 88%).

The highest ascertainment to NCAS was from the regions covered by NTW and WANDA and the lowest from the OXCAR area. However, ascertainment was not consistent when individual defects were compared.

The proportion of cases ascertained by NCAS varied little by area deprivation, certainly less than could be explained by chance (P > 0.1). This pattern did not change on adjustment for differences in ascertainment by registry and hospital catchment area.

Discussion

Surveillance of congenital anomalies in England is currently inadequate. NCAS identified only 40% of the live and stillborn cases it was set up to survey. Moreover, NCAS identified little more than a quarter of all cases including terminations, which are now numerically important in England. Whether terminations were included or excluded, case ascertainment, while always low, varied by anomaly, register, and hospital catchment area. Anomalies obvious at birth (such as cleft lip, limb defects) are more likely to be ascertained than "hidden" defects (such as renal anomalies, cardiac defects). Under-ascertainment by NCAS has long been known to be a problem.

Purpose of surveillance and deficiencies of the current system
The original and main purpose of the NCAS is surveillance over time. However, there is no way of knowing whether an increase in notification is due to improved ascertainment or to a true increase in incidence. Furthermore, for other uses of the data constant ascertainment over time does not ensure against bias due to under-ascertainment.

In an attempt to redress the deficiencies, electronic transmission of data on live births and stillbirths from some registers (Wales and Trent) to the national register was instituted in 1998 and 1999 and from others, including those participating in this study, more recently. This will presumably bring the standard of national registration of live births and stillbirths to that of local registries where these exist. However, at present only 50% of births in England are covered by local registers.

Impact of terminations
Given that for some anomalies (Down's syndrome, neural tube defects) most pregnancies with affected fetuses in England result in termination of pregnancy,^{6 7} the lack of data on termination of pregnancy in NCAS is an important omission. A change in the NCAS system to record these data would result in a much more valuable data set.

Impact of poor national data
The poor quality of NCAS data has implications for the interpretation of epidemiological studies seeking to establish risks of congenital anomaly related to residence in relation to environmental pollution sources.⁸ It is reassuring that we could find no ascertainment bias in relation to socioeconomic deprivation. However, given the high level of variation in ascertainment between hospital catchment areas, we recommend that a minimum requirement in using these data is to take this into account in statistical analyses.

Impact of local data
It is not surprising that local registers have more complete and accurate data than those on the national register, given the active ascertainment of cases from multiple sources. A hierarchical system of local data collection, which feeds into a national register (as is the case for cancer registration), should be the most effective model of national surveillance. However, for this system to work it would be necessary for the whole population to be covered by local registers. This does not necessarily mean that all local registers should follow the same model—some may be more research oriented than others, particularly with regard to aetiological factors—but we recommend a basic surveillance dataset.

Outlook
If it is important to conduct surveillance of congenital anomalies to look for associations with potential environmental teratogens, to support health service planning, and to monitor prenatal diagnosis and screening programmes, then ascertainment of defects at national level must be improved. We support moves to obtain data from local registers, to extend coverage of local registers to the whole country, and to institute an effective national data collection system for terminations of pregnancy.

What is already known on this topic The National Congenital Anomaly System (NCAS) is the basis for surveillance of congenital anomalies in England and Wales Ascertainment of cases by NCAS is incomplete What this study adds The surveillance of congenital anomalies in England is currently inadequate because ascertainment of affected live and still births by the national register is very low (40%), varying by defect, region, and hospital and because NCAS currently does not include data on terminations of pregnancy after prenatal diagnosis of fetal anomaly

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This is the abridged version of an article that was posted on bmj.com on 23 November 2004: http://bmj.com/cgi/doi/10.1136/bmj.38300.665301.3A

We acknowledge the support of staff in the congenital anomaly registries, all those who contributed cases and help in data preparation from Michael Rosato, Chris Dunn, Chris Grundy and Nigel Physick.

Contributors See bmj.com

Funding: DH/DETR/Environment Agency Joint Research Programme on the possible health effects of landfill sites.

Competing interests: None declared.

Ethical approval: London School of Hygiene and Tropical Medicine ethics committee. In addition, each of the four local registers have approval from their local multicentre research ethics committee (reference number 04/MRE04/25).

References

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3. Office for Population Censuses and Surveys. The OPCS monitoring scheme for congenital malformations occasional paper 43. A review by a working group of the registrar general's medical advisory committee. London: OPCS, 1995.
4. Busby A, Dolk H, Collin R, Barry Jones R, Winter R. Compiling a national register of babies born with anophthalmia/microphthalmia in England 1988-94. Arch Dis Child Fetal Neonatal Ed 1998;79: F168-73.[Abstract/Free Full Text]
5. Dolk H, Armstrong B, Vrijheid M, Stone D, Rankin J, Abramsky L, et al. A study of the geographical variation in overall rates of congenital abnormalities and the rates of specific abnormalities. Report to Department of Health, 2003. www.eurocat.ulster.ac.uk/pubdata (accessed 16 Nov 2004).
6. National Down syndrome cytogenetic register 2002 annual report. London: NDSCR, 2003. www.smd.qmul.ac./wolfson/ndscr/NDCSRreport.pdf (accessed 3 Nov 2004).
7. Hey K, O'Donnell M, Murphy M, Jones N, Botting B. Use of local neural tube defect registers to interpret national trends. Arch Dis Child 1994;71: F198-F202.
8. Elliott P, Briggs D, Morris S, de Hoogh C, Hurt C, Jensen TK, et al. Risk of adverse birth outcomes in populations living near landfill sites. BMJ 2001;323: 363-8.[Abstract/Free Full Text]

(Accepted 16 October 2004)

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