Cohort studies are usually based on detailed information gathered on a limited number of individuals. Increasing collection of administrative registers offers an alternative method to gather health data. In the first study health information from birth until the age of seven years on 8708 children born in the two most northern provinces of Finland in 1985-86 was gathered through questionnaires, medical record reviews, medical examinations and some register data. In the second study, similar information on 8222 children born in the same provinces in 1987 was gathered using administrative registers. Both data collection methods gave equal results for mortality, long-term medication. and cumulative incidence of diabetes and intellectual disabilities. The register data identified more children with delayed development, but less children with long-term illness (77% of the level identified by the research data), with asthma (74%), and with epilepsy (40%). The register data was unsuitable for investigating hearing and vision disorders. The administrative data gave a gender ratio similar to that of the research data for two of the variables with poor coverage (asthma and epilepsy), but identified more boys with long-term illness in general than the research data. Administrative registers are useful for studying many long-term health problems, e.g. those resulting in hospital care or social benefits or those registered in vital statistics. Specific cohort studies with separate data collection is still needed to study for example outpatient care, self-assessed health, growth and development.
The validity of the 1991 Finnish Medical Birth Registry data was assessed, with special emphasis on the effects of changes made to the data collection form in 1990. Data abstracted from medical records for all births occurring in 49 hospitals during a five-day sample period (n = 865) were compared to the register information. Good or satisfactory validity was found for 32 of 33 variables, when minor error was tolerated in variables with continuous scales. For diagnoses and procedures, recorded in check-box format, satisfactory validity was found for 10 of 45 variables. Validity could not be assessed for 18 variables because of insufficient number of cases (13 items) or definition problems (5 items). When the results were compared to a 1987 data quality study, many of the variables that had been changed to the check-box format showed improvement in validity. In addition, in some cases a small change in question alternatives or instructions caused a noticeable change in validity.
Induced abortion rates have declined in Finland since 1973. A possible explanation offered has been that of deteriorating data collection.
To assess the completeness of the Register, we compared the information from a consecutive sample of hospital records (N = 482) to the Finnish Abortion Register in 18 hospitals in three counties. A smaller consecutive sample (N = 345) was collected from the same hospitals to assess the validity of the Register information.
Only five abortions (1 percent) found in the hospitals were not reported in the Abortion Register. A total of 95 percent of all the length of pregnancy (definition problems), the classification of the abortion procedure, and social class (out-of-date classifications). Furthermore, early complications were poorly reported.
The data from the Finnish Abortion Register are a reliable source for monitoring trends in the abortion rate and its variation by subgroups, but are an unreliable source for the study of the medical aspects of induced abortion.
Follow-up studies on health have usually been based on ad hoc cohort studies in which detailed information is collected specifically for research purposes on a certain group of people. The increasing collection of routine health data provides an alternative method of gathering follow-up data. In this study, the feasibility of using routinely collected health-register data and data linkages to follow up children's health was investigated. Five nationwide registers, 18 regional registers of intellectually disabled children and school administration data in one county were found to be of use for our follow-up and were combined with the 1987 Finnish Medical Birth Register (n = 60,254 births). In the follow-up, 62 children were untraced (0.1%), 327 were stillborn (0.5%), 440 died after birth (0.7%) and 287 emigrated (0.5%) before the age of 7 years. The cumulative incidences for all diseases (8.9% of all children living in Finland at the age of 7 years), for diabetes (3.0/1000), for epilepsy (6.8/1000) and for asthma (34.2/1000) correspond to the estimates of other studies, but our estimate for intellectual disabilities (18.0/1000, of whom 18% were reported to have an IQ of 70 or less) seems to be an underestimate. Our data collection did not provide reliable information on institutionalised children or children taken into care. Data collection conducted by using health registers is a feasible method, and it saves both time and financial resources compared with cohort studies. Potential problems with data linkage studies are variation in the content of data and in data quality of different registers and data protection issues.
Two problems originating from the advanced use of medical technology in screening for malformations and in the care of preterm and low birthweight infants are presented: the impact of the increasing number of induced medical abortions and the differences in statistical definitions on perinatal mortality (PNM) figures. Data on 186,562 births registered in the Finnish Medical Birth Registry between 1987 and 1989 were studied, and 65,554 medical abortions (of which 1647 were performed after the sixteenth week of gestation) registered in the Abortion Registry between 1985 and 1990. A 115% increase in abortions for medical reasons in the period 1985-1990 was found. It was estimated that the trend accounted for up to one-third of the decline in PNM rate during that time. The perinatal mortality rate was strongly influenced by very small infants. The application of the Finnish version of the International Classification of Diseases, Ninth Revision (ICD-9) (including all livebirths and using both birthweight of 500 g and gestational age of 22 weeks as the criteria) resulted in PNM rates which were about 5% higher than according to ICD-9. We suggest that the impact of medical abortions on perinatal statistics has reduced the value of the perinatal mortality rate as an indicator of the standard of care.
Several studies on differences in infant outcome by socioeconomic position have been done, but these have usually been based on ad hoc data linkages. The aim of this paper was to investigate whether socioeconomic differences in perinatal health in Finland could be regularly monitored using routinely collected data from one single register.
Since October 1990, the Finnish Medical Birth Register (MBR) has included data on maternal occupation. A special computer program that converted the occupation name into an occupational code and into a socioeconomic position was prepared. Perinatal health was measured with five different indicators. The Finnish MBR data for years 1991 to 1999 (n=565 863 newborns) were used in the study. The study period was divided into three, three year periods to study time trends.
An occupational code was derived for 95% of women, but it was not possible to define a socioeconomic position for 22% of women, including, for example, students and housewives (the group "Others"). For the rest, the data showed socioeconomic differences in all perinatal health indicators. Maternal smoking explained up to half of the excess risk for adverse perinatal outcome in the lowest socioeconomic group. The socioeconomic differences narrowed during the 1990s: infant outcome improved in the lowest socioeconomic group, but remained at the same level or even deteriorated in other groups. When comparing the lowest group with the highest group, the odds ratios (OR) adjusted for maternal background characteristics at least halved for prematurity (from 1.32 (95% confidence intervals 1.24 to 1.43) in 1991-1993 to 1.16 (1.08 to 1.25) in 1997-1999), for low birth weight (from 1.49 (1.36 to 1.63) to 1.25 (1.17 to 1.40)), and for perinatal mortality (from 1.79 (1.44 to 2.21) to 1.33 (1.07 to 1.66)).
Social inequality in perinatal health outcomes exists in Finland, but seems to have diminished in the 1990s. These data showed that routinely collected birth register data provide a good source for studies on socioeconomic health differences in the perinatal period, but that uncertainty, mainly attributable to the large group of women with difficult to classify socioeconomic status, remains.