Reporting of malformations in routine health registers.

The utility of three national registers--the malformation, birth, and hospital in-patient discharge registers--in identification of malformations among 60,255 children born in 1987 in Finland was compared. Information in the malformation register is collected by specific reporting of physicians; information on the malformed children in the other two registers in 1987 through 1990 was routinely collected and identified by ICD 9-codes (740-759, 7886A). From October 1990 on, the ICD-9 codes were omitted from the birth register and malformation data were asked only in a yes-no question. In 1987, the malformation register included 1,032, the birth register 3,084 and the in-patient register 2,003 malformed infants identified up to the age of 1 year. There was underrepresentation of almost all malformation diagnoses in the malformation register. Individual linkage of the three registers showed that the malformation register revealed very few cases not recorded in the birth and the in-patient registers. With the adoption of the new recording method in the birth register beginning in October 1990, reports of malformation declined by 75%. Our analyses showed that data sources based on diagnoses collected routinely and not requiring an explicit decision on whether or not a problem is a malformation, can be more useful for routine surveillance of occurrence of malformations.