Narrowing inequalities in infant mortality in Southern Brazil

Correspondence to: Marcelo Zubaran Goldani Departamento de Pediatria e Puericultura Faculdade de Medicina (UFRGS) Avenida Ramiro Barcellos, 2400 90035-003 Porto Alegre, RS, Brazil E-mail: hegold@uol.com.br Supported by “Fundação de Amparo à Pesquisa do Rio Grande do Sul” (FAPERGS Process no 1077/99-0). Carried out in the “Departamento de Pediatria e Puericultura da Faculdade de Medicina da Universidade Federal do Rio Grande do Sul” and “Hospital de Clínicas de Porto Alegre”. Received on 1/10/2001. Reviewed on 19/3/2002. Approved on 8/4/2002.


INTRODUCTION
Despite a steady decrease in infant mortality in Brazil from 52.0/1,000 in 1989 to 36.1/1,000 in 1998, 6 the country has one of the highest levels of socioeconomic inequality in mortality of children under 5year old. 15Also, a strong association between low maternal social status and higher infant mortality rates has been well documented. 3,5,11However, there is scarce information about the trends of social inequalities in infant mortality in the country.One of the reasons for that is the poor quality of data regarding socioeconomic variables in registry sources.
A new municipal database, the SINASC (Sistema de Informação sobre Nascidos Vivos -Live Births Information System), was set up in order to collect systematic information about mothers and anthropometric measurements of newborns in the early 1990s. 10nformation on infant deaths has been obtained by the SIM (Sistema e Informações sobre Mortalidade -Mortality Information System) since the late 1970s.
Nevertheless, the available data has not been much analyzed and its application in defining the scale of inequality in health is hardly explored.The aim of this study was to analyze the trends of infant mortality in Porto Alegre, South Brazil, using information routinely available at the municipal level and a geographic area-based measure of maternal education.The following issues were raised: did infant mortality rate reduce from 1995 to 1999?If so, was the reduction steeper for the post-neonatal or the neonatal component?Were there inequalities in infant mortality?If so, were they evident for both components?Did inequalities show evidence of reduction from 1995 to 1999?Were they still noticeable in 1999?

METHODS
A registry-based study was carried out in the city of Porto Alegre, South Brazil.All live births and deaths data of the same group of children during their first year of life in the period between 1995 and 1999 were col-lected.A total of 119,170 live births and 1,934 infant deaths occurred from 1995 to 1999 in 82 districts of Porto Alegre.The number of deaths was obtained from the SIM, where virtually all deaths in the city are reported. 10This database provides a systematic collection of death certificates from all registry offices, providing the annual number of deaths from different areas of the city.Death reporting in Porto Alegre follows nationally determined convention based on international norms.
The number of live births and percentage of mothers with educational level under six years of schooling in each urban district were obtained from the SINASC, a database based on birth certificates from all births in the city. 7Since 1994, this database provides information about hospital deliveries, which are estimated to correspond to 99% of all deliveries in the city.Missing data of maternal educational level was 0.6% of all live-births.
Information about home deliveries was obtained monthly by consulting all registry offices in the city.Under enumeration of births has been estimated in 0.1% of all live-births.Deaths and live-births were analyzed independently as there was no link between the two systems.
Complete information about family addresses in the urban area of Porto Alegre was included in both databases, so the location of each family in each administrative urban area could be found.
It was used a geographic area-based measure of maternal education.Urban districts of the city were divided in five groups according to their percentage of mothers with low educational level (less than six years of schooling).Percentages corresponding to each district were sorted out and a quintile distribution was created.The five district groups were classified as high, medium high, medium, medium low and low based on their level of maternal education.Infant mortality rate (IMR) and its components, neonatal mortality rate (NMR) and post-neonatal mortality rate (PNMR), were determined for each area in the study period.Chi-square test for trend was applied to indicate trends in infant mortality rates according to area for each year.The excess of infant mortality rate per area was demonstrated using the incidence rate ratio (IRR) calculated by Poisson regression with 95% confidence interval, contrasting medium low and low with medium high and high areas.Areas were collapsed to increase precision of the estimates.

RESULTS
The largest number of live births and deaths occurred in low and medium low areas of maternal schooling.
The trend remained constant over the five years (Table 1).Neonatal deaths tended to predominate in all areas, although post-neonatal deaths were the most important in low, medium low and medium areas in some years (Table 2).
Infant mortality rate declined steadily from 1995 to 1999.IMR also decreased significantly in low and medium areas.Both neonatal and post-neonatal mortality rates decreased although the drop seemed to be steeper for the post-neonatal component.The low area showed a significant reduction in both neonatal and postneonatal components over the study period.A significant drop in post-neonatal mortality rate was also observed for medium low area.Mortality rates in medium high and high areas showed little variation (Table 2).
There was a significant improvement in the percentage of mothers with less than 6 years of schooling in all areas (Table 3).Comparing 1995 to 1999   there was a significant decrease in the contribution of low (from 28.9% to 24.2%), medium (from 20.1% to 13.1%), and high areas (from 11.8% to 11.4%) of maternal schooling in the total of live births (p-value for trend <0.001).An increase of live births in medium low (from 25.8% to 40.5%) and medium high (from 13.3% to 10.9%) maternal schooling areas was also evident (p-value for trend <0.001 -percentages not shown in the table ).
Table 4 depicts incidence rate ratio estimates for neonatal, post-neonatal and infant mortality, according to a geographic area-based measure of maternal education, contrasting low and medium low areas with medium high and high areas between 1995 and 1999.An estimate for the entire period and a p-value for trend across all quintiles were also calculated.A statistically significant difference between low and high areas was evident for infant, neonatal and postneonatal mortality when the five years were considered together (Table 4).
IMR and post-neonatal mortality rates tended to increase from high to low areas in all years except for 1999.Neonatal mortality rates increased from high to low areas only in 1996 (Table 4).The excess of infant mortality in low areas compared to high areas dropped from 1.71 (71%) in 1995 to 1.22 (22%) in 1999 probably due to a higher decline of deaths in low areas over the period.However, the difference between high and low areas remained statistically significant until 1998.The differentials between areas were larger in the post-neonatal period and smaller or even absent in the neonatal period (Table 4).
Inequalities in post-neonatal mortality decreased in the study period.However, inequalities in neonatal mortality seemed to be smaller and had little variation over time.Inequalities in IMR, NMR, and PNMR were not statistically significant at the end of the time series in 1999 (Table 4).

DISCUSSION
Maternal educational level related to persistent social inequalities has been used to discriminate social differences and measure their impact on infant health. 14,17 the case of Porto Alegre, the adjusted model, using a geographic area-based measure of maternal education, demonstrated significant disparities in terms of infant mortality among five different areas.There seem to have been a more accentuated decline in infant mortality in the less privileged areas, and a reduction in IMR inequalities, despite overlapping confidence intervals in comparisons between years.Differentials between areas were larger in the postneonatal period and smaller or absent in the neonatal period, corroborating other studies. 16e fact that inequalities in neonatal and postneonatal mortality were not evident in 1999 might have been due to small sample size.If more births and deaths had occurred, a significant difference between areas might have arisen.The power to detect an excess of 50% in mortality in low and medium low areas (exposed) in relation to medium high and high areas (unexposed) was 86.1% in 1999.However, the power decreased to 64.1% for a 40% excess risk and to 34.7% for a 30% excess risk in infant mortality.
Inequalities in neonatal mortality were only observed in 1996.This is less likely to be explained by random variability but this possibility could not be entirely ruled out.
There are some difficulties in using geographic areabased measures as a parameter for urban social inequality.There are demographic similarities between district borders.Also, large geographic areas may have low demographic homogeneity whereas geographic areas with large random variability of events can make it difficult to identify districts at risk. 1 A significant decrease in the percentage of live births in districts with high prevalence of low maternal education as a total of live births was observed.This may be interpreted as either a drop in births of low maternal schooling mothers or an improvement of social conditions, or both.In fact, levels of illiteracy in Brazil declined from 17.0% in 1995 to 15.1% in 1999 18 and a decrease in the percentage of low schooling mothers among all births has been observed in the city of Pelotas. 2 Three main factors can explain this steady decline in IMR, mainly in its post-neonatal component.2][13] These changes could have positively influenced a sustained improvement of living standards and a more accelerated reduction in neo and post-neonatal mortality of the two less privileged groups from 1996 onwards, contributing to decrease social inequalities in IMR.
The second factor could be a positive impact on neonatal mortality rates of synthetic surfactant therapy for respiratory distress syndrome. 4Its use was introduced in public hospitals in Porto Alegre in the early 1990s.Since the speed of decline of neonatal mortality seemed to be similar in all areas, it appears that access to perinatal and neonatal care is universal in the city.
Thirdly, the mild decline in infant mortality in more privileged areas might also be accounted for by their lower infant mortality rate, which would have reached the limits of local health technology.Similarly, further improvements in environmental conditions and maternal educational level may have had a smaller impact in better-off groups.
There could be another possible explanation.Live births of those who died just after delivery could have been underreported or misclassified as stillbirths.This possible bias could have occurred mainly in less privileged groups and in newborns weighing less than 1500 g, overestimating the decrease in neonatal mortality in these groups. 8However, comparison between infant mortality coefficients from official database and from other sources did not reveal significant differences, making this hypothesis unlikely. 9 conclusion, the findings revealed a positive trend towards a reduction in infant mortality.The reduction seemed to have been greater for the post-neonatal component.The reduction of infant mortality rate seemed to be steeper in less privileged areas, especially in the post-neonatal period, despite the higher prevalence of low maternal educational.Differentials between areas were larger in the post-neonatal period and smaller or absent in the neonatal period.Although the small number of deaths in some areas made a more definite conclusion difficult, it seems there is a decrease of IMR inequalities in different geographic areas of Porto Alegre.

Table 2 -
Neonatal mortality rate, post-neonatal mortality rate and infant mortality rate (per thousand) from 1995 to 1999 according to geosocial class in Porto Alegre, Brazil, 1995/1999.

Table 3 -
Percentage of mothers with less than sic years of schooling in each quintile per year in Porto Alegre, Brazil.

Table 4 -
Incidence rate ratio for neonatal, post-neonatal and infant mortality according to geosocial class and year.