Ao estudar um tema, frequentemente nos deparamos com resultados contraditórios. Um caminho coerente para tentar esclarecer controvérsias é apoiar-se apenas nos estudos de melhor qualidade sobre o assunto. Partindo desse princípio, surgiu um novo delineamento de pesquisa: a revisão sistemática da literatura. Trata-se de um tipo de investigação focada em questão bem definida, que visa identificar, selecionar, avaliar e sintetizar as evidências relevantes disponíveis.A atividade de compilar dados científicos sobre um tema é praticada na área da saúde há muito tempo. Uma das primeiras revisões de que se tem registro data de 1753, e foi feita por Sir James Lind sobre a prevenção e o tratamento do escorbuto. 1 Por sua vez, a primeira soma estatística dos resultados de estudos, técnica hoje conhecida como metanálise, foi publicada em 1904 pelo matemático Karl Pearson. 2 As revisões que podemos considerar como sistemáticas começaram a aparecer na década de 1950. No entanto, o desenvolvimento metodológico dessas pesquisas na área da saúde só se consolidou ao fim da década de 1980. Foram marcos nesse processo a publicação do livro Effective care during pregnancy and childbirth e, na década seguinte, a criação da Colaboração Cochrane, em Oxford, Reino Unido. 3,4 As revisões sistemáticas devem ser abrangentes e não tendenciosas na sua preparação. Os critérios adotados são divulgados de modo que outros pesquisadores possam repetir o procedimento. Revisões sistemáticas de boa qualidade são consideradas o melhor nível de evidência para tomadas de decisão. Por seguir um método científico explícito e apresentar resultado novo, a revisão sistemática é classificada como contribuição original na maioria das revistas de pesquisa clínica. 5 As revisões sistemáticas diferem das revisões narrativas ou tradicionais. Essas são amplas e trazem informações gerais sobre o tema em questão, sendo comuns em livros-texto. Também se distinguem das revisões integrativas, nas quais se utilizam diferentes delineamentos na mesma investigação, além de expressarem a opinião do próprio autor. 6 Nesta série de artigos na Revista Epidemiologia e Serviços de Saúde, apresentaremos os principais cuidados quanto à elaboração de revisões sistemáticas, fornecendo ao leitor fontes de informação adicionais para aprofundamento no assunto.

Objective: To systematically analyze the relationship between maternal anemia and low birth weight. Methods: A search of studies was conducted in the main databases (Medline, Embase, Scopus, Web of Science, SciELO, and Lilacs), the gray literature, and the reference lists of selected articles. Cohort and case-control studies that met the eligibility criteria were included in the review. There was no limitation on the language or date of publication. Article selection and data extraction were performed by two independent reviewers. Meta-analyses with random effects, subgroup analyses and meta-regressions were performed. Publication bias was measured using Egger regression and visual funnel plot inspection. Results: A total of 7243 articles were found, of which 71 comprised the systematic review and 68 were included in the meta-analyses. Maternal anemia was associated with low birth weight with an adjusted OR: 1.23 (95% CI: 1.06–1.43) and I2: 58%. The meta-regressions confirmed that the sample size and the methodological quality may partially explain the statistical heterogeneity. Conclusions: Maternal anemia was considered a risk factor for low birth weight.

Objective To conduct a systematic review and meta‐analysis to evaluate the recent scientific literature addressing the association between periodontitis and asthma, chronic obstructive pulmonary disease (COPD), and pneumonia. Materials and Methods The search for studies was carried out using MEDLINE/PubMed, EMBASE, Lilacs, Web of Science, Scopus, and SciELO databases, including the gray literature (ProQuest). Reference lists of selected articles were also searched. Studies having varying epidemiological designs assessing the association between periodontitis and respiratory diseases in human subjects were eligible for inclusion. Three independent reviewers performed the selection of articles and data extraction. Fixed and random effects meta‐analysis were performed for the calculation of the association measurements (Odds Ratio—OR) and 95% confidence intervals (95% CI). Results A total of 3,234 records were identified in the database search, with only 13 studies meeting the eligibility criteria and 10 studies contributed data for meta‐analysis. Using a random effects models periodontitis was associated with asthma: ORadjusted: 3.54 (95% CI: 2.47–5.07), I2 = 0%; with COPD: OR adjusted: 1.78 (95% CI: 1.04–3.05), I2 = 37.9%; and with pneumonia: OR adjusted: 3.21 (95% CI: 1.997–5.17), I2 = 0%. Conclusions The main findings of this systematic review validated an association between periodontitis and asthma, COPD and pneumonia.

BackgroundCountries in Latin America and the Caribbean (LAC) have experienced a rapid increase in their proportion of older people. This region is marked by a high prevalence of chronic diseases and disabilities among aging adults. Frailty appears in the context of LAC negatively affecting quality of life among many older people.AimTo investigate the prevalence of frailty among community-dwelling older people in LAC through a systematic review and meta-analysis.MethodsA literature search was performed in indexed databases and in the grey literature. Studies investigating the prevalence of frailty with representative samples of community-dwelling older people in Latin America and the Caribbean were retrieved. Independent investigators carried out the study selection process and the data extraction. A meta-analysis and meta-regression were performed using STATA 11 software. The systematic review was registered at the International Prospective Register of Systematic Reviews under the number CRD42014015203.ResultsA total of 29 studies and 43,083 individuals were included in the systematic review. The prevalence of frailty was 19.6% (95% CI: 15.4–24.3%) in the investigated region, with a range of 7.7% to 42.6% in the studies reviewed. The year of data collection influenced the heterogeneity between the studies.ConclusionFrailty is very common among older people in LAC. As a result, countries in the region need to adapt their health and social care systems to demands of an older population.

A previous search of the major electronic databases revealed that no studies appear to have been conducted to summarize the association between maternal active smoking during pregnancy and low birth weight within the Americas. Therefore, this systematic review may help to fill the information gap. The region of the Americas contains some of the most populous countries in the world; therefore, this study may provide useful data from this massive segment of the world's population.