Ascertainment of pregnancies terminated because of birth defects: Effect on completeness of adding a new source of data

Background: When evaluating preventive programs such as folate promotion an d rubella vaccination, it is critically important to include terminations o f pregnancy for neural tube defects and congenital rubella syndrome. Data f rom birth defects registries are often used for this purpose. The Western A ustralian Birth Defects Registry ascertains cases of birth defects in liveb irths, stillbirths, and terminations of pregnancy for fetal abnormality, us ing multiple sources of ascertainment. Methods: Data on terminations of pregnancy for fetal abnormality from the W estern Australian Hospital Morbidity Data System 1980-1997 (not previously available to the Registry) were used to estimate the completeness of ascert ainment of such cases by the Registry. Ascertainment-adjusted prevalences w ere calculated using capture-recapture methods. Results: A total of 702 terminations with birth defects were identified amo ng hospital discharges, most of which were already known to the Registry (8 7.9%). Of the 85 new cases, seven had a neural tube defect, 23 had a chromo somal defect, and 12 had confirmed maternal rubella infection during pregna ncy. The ascertainment-adjusted prevalence was not significantly different for birth defects overall or for these individual conditions, although the 95% confidence intervals for all birth defects, and for all chromosomal def ects, did not include the prevalence based on registered cases only. Conclusions: The Western Australian Birth Defects Registry ascertains a hig h proportion of pregnancies terminated for fetal abnormality, and should th erefore be a reliable source of data with which to assist in monitoring the effectiveness of preventive programs. Teratology 63:23-25, 2001. (C) 2001 Wiley-Liss, Inc.