Brazilian Journal of Medical and Biological Research (2007) 40: 1203-1210 Smoking during pregnancy in two Brazilian cities ISSN 0100-879X
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Do socioeconomic factors explain why maternal smoking during pregnancy is more frequent in a more developed city of Brazil? V.S. Ribeiro1, F.P. Figueiredo2, A.A.M. Silva2, R.L.F. Batista2, M.A. Barbieri3, F. Lamy Filho1, M.T.S.S.B. Alves2, A.M. Santos2 and H. Bettiol3
1Departamento
de Medicina III, 2Departamento de Saúde Pública, Universidade Federal do Maranhão, São Luís, MA, Brasil 3Departamento de Puericultura e Pediatria, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brasil
Abstract Correspondence V.S. Ribeiro Rua dos Rouxinóis Condomínio Alphaville Bloco 2, Apto. 402, Renascença II 65075-630 São Luís, MA Fax: +55-98-3235-3020 E-mail:
[email protected] Research supported by FAPESP (No. 93/0525-0) and CNPq (Nos. 523474/96-2 and 520664/98-1).
Received October 10, 2006 Accepted June 4, 2007
The prevalence of smoking during pregnancy in Ribeirão Preto, a rich Brazilian city, was significantly higher (21.4%) than in São Luís (5.9%), a less developed city. To assess which variables explain the difference in prevalence of smoking during pregnancy, data from two birth cohorts were used, including 2846 puerperae from Ribeirão Preto, in 1994, and 2443 puerperae from São Luís, in 1997/98. In multivariable analysis, risk of maternal smoking during pregnancy was higher in São Luís for mothers living in a household with five or more persons (OR = 1.72, 95%CI = 1.12-2.64), aged 35 years or older (OR = 1.98, 95%CI = 0.99-3.96), who had five or more children (OR = 2.10, 95%CI = 1.16-3.81), and whose companion smoked (OR = 2.20, 95%CI = 1.52-3.18). Age of less than 20 years was a protective factor (OR = 0.55, 95%CI = 0.33-0.92). In Ribeirão Preto there was association with maternal low educational level (OR = 2.18, 95%CI = 1.30-3.65) and with a smoking companion (OR = 3.25, 95%CI = 2.524.18). Receiving prenatal care was a protective factor (OR = 0.24, 95%CI = 0.11-0.49). Mothers from Ribeirão Preto who worked outside the home were at a higher risk and those aged 35 years or older or who attended five or more prenatal care visits were at lower risk of smoking during pregnancy as compared to mothers from São Luís. Smoking by the companion reduced the difference between smoking rates in the two cities by 10%. The socioeconomic variables in the model did not explain the higher prevalence of smoking during pregnancy in the more developed city.
Introduction The relation between smoking during pregnancy and the occurrence of perinatal complications has been clearly demonstrated
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Key words • • • • •
Smoking Pregnancy Risk factors Perinatal complications Placenta previa
in the literature. Smoking mothers have more preterm deliveries (1), children with intrauterine growth restriction (2), preterm rupture of membranes (3), placental abruption (4), placenta previa (5), and infections dur-
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ing pregnancy (6). Intrauterine exposure to tobacco is also directly related to an increased risk of stillbirth and of death during the first year of life (6,7), to sudden death syndrome in infancy (6), and to a higher risk of death during later stages of childhood (8,9). The prevalence of smoking during pregnancy in developed countries was 25% in France in 1988 (2) and 18% (among whites) and 14% (among blacks) in the United States throughout the 1990 decade (10). In Brazil, smoking during pregnancy varies widely, with a prevalence of 7.2% in Manaus (North), 16.8% in Fortaleza (Northeast), 16.1% in São Paulo (Southeast), and 31.9% in Porto Alegre (South) (11). In the 1990 decade, the prevalence in Pelotas (State of Rio Grande do Sul, South) was 33.2% (12), with this percentage reaching 44.2% at the beginning of pregnancy (13). In Brazilian studies, among the factors that have been related to smoking during pregnancy particularly important are low schooling, multiparity, the consumption of alcoholic drinks, a smoking companion (11), low income, and absence of prenatal care (14). To our knowledge, no study has been designed to investigate why maternal smoking rate during pregnancy is higher in more developed Brazilian cities and to what extent socioeconomic inequalities are able to explain the difference in rates. The aim of the present study was to investigate if socioeconomic factors explain why maternal smoking during pregnancy is higher in Ribeirão Preto (21.43% in 1994), a more developed city located in the Southeast (15), than in São Luís (5.94% in 1997/98), a less developed municipality in the Northeast of Brazil (16).
Material and Methods The data used in the present investigation were obtained from two birth cohort studies conducted in São Luís, State of Maranhão Braz J Med Biol Res 40(9) 2007
(MA), in 1997/98 and in Ribeirão Preto, State of São Paulo (SP), in 1994. Systematic sampling stratified according to the maternity hospital was used in São Luís. The study covered 94% of all hospital births during a period of one year and was carried out at public hospitals of the Unified Health System (SUS in the Portuguese acronym), and at hospitals covered by insurance and/or private. One seventh of the deliveries that occurred during a period of 1 year, from March 1, 1997 to February 28, 1998, including resident and non-resident subjects, liveborns or stillborns and singletons or multiple births were investigated. Only data concerning residents and liveborn singletons were included in the present study. A questionnaire was applied to the puerperae, usually soon after delivery, after they gave informed consent. The questionnaire contained identification, demographic and socioeconomic data, as well as questions about reproductive health and utilization of prenatal services. A total of 2443 observations were recorded, with a 5.9% prevalence of maternal smoking being identified (16). In Ribeirão Preto, information was collected from all puerperae over a period of four consecutive months (one third of all deliveries) from April 25 to August 25, 1994. This collection was based on a previous study showing that there was no seasonality of births along the year or of some of the other variables considered in the study (e.g., low birth weight, preterm birth, maternal age at delivery, and multiple births) (15). Considering only liveborn singletons from families residing in the municipality, the sample consisted of 2846 births, and a 21.4% prevalence of maternal smoking was identified (15). The study covered 98% of all births that occurred in the city during the study period. The methodological procedures of the two studies have been described in detail in other publications (15-17). The study variables were analyzed separately in each city both in the non-adjusted www.bjournal.com.br
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and adjusted model. The factors associated with maternal smoking were first identified using a simple logistic regression model (18). For the construction of the adjusted model, a model containing all the selected variables that might be related to maternal smoking was used as the starting point. Next, the joint logistic model with the two cities in the same model was considered, including the “city” variable, which was coded as 1 = Ribeirão Preto and 0 = São Luís. The interactions between the study site and the remaining factors selected were tested and those found to be statistically significant were included in the final model together with the main effects. Finally, a combined sequential model was analyzed. The crude odds ratio (OR) of maternal smoking was calculated according to “city” to estimate the non-adjusted difference in the maternal smoking rate during pregnancy between the two towns. Next, each variable was adjusted together with the “city” variable, and this adjusted OR was compared to the crude OR. If the variable reduced the adjusted OR compared to the crude OR by at least 10%, it was considered to explain some of the difference in maternal smoking rate between the two towns. At the end, the adjusted OR was calculated for all variables studied. Data were analyzed using the Stata statistical package, version 8.0 (19). P values
