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Critical Appraisal Most studies that report estimates of prevalence are specifically designed to do so and have it as the primary aim of the study Before accepting the results of these studies, it is important critically to appraise the methods and reporting, to determine if the findings are valid, reliable, and relevant Critical appraisal is also required when one wishes to compare estimates arising from different studies, such as comparisons of trends over time or across different populations Consideration must be given to all of the aspects by which the denominator and numerator are defined and derived and to the adequacy of reporting of the associated methods and results In Box 13.1, questions for which the answers should be evident when critically appraising a report regarding prevalence are noted Box 13.1 Questions for Critically Appraising a Report About Prevalence ▪ What was the stated purpose or aim of the study? ▪ How accurate and valid was the estimate reported? ▪ How accurate and valid was the definition and completeness of the numerator? ▪ What forms of congenital heart disease were included or excluded? ▪ What nomenclature and system of classification was used to describe and group cases? ▪ What were the methods by which cases were ascertained and reported? ▪ What was the overall design of the study and data collection? ▪ How were cases detected and reported from the population studied? ▪ What factors, particularly relating to the system for health care, may have influenced the ascertainment of cases? Specifically, did everyone in the population studied have equal access to health care and the referral center, and was screening and verification influenced by differences in quality and availability of expertise or technology? ▪ How were diagnoses confirmed or verified? ▪ How long was the follow-up, and was it sufficiently long to capture cases with later clinical manifestation? ▪ If a universal screening was applied, was it applied equally to the entire population at an early enough time point, was it sufficiently sensitive and specific, and was an assessment of verification performed? ▪ How accurate and valid was the definition and completeness of the denominator? ▪ What was the definition of the population studied? ▪ What were the sources of data used to derive the denominator, and were they valid and reliable? ▪ How accurately and completely does the population studied reflect the target population or population at large? ▪ Are the cases completed derived from the population studied as defined in the denominator? Were the cases and population characterized as part of the same study with the same methodology, as in a cohort study? ▪ How reliable is the estimate of prevalence estimate? Are confidence intervals provided? ▪ How does the estimate from the study compare with those reported from other studies with comparable methodology? ▪ Is the estimate applicable to your own clinical population? Is the population studied similar to your own clinical population in terms of setting, time, geography, and demographic characteristics? Is the estimate of prevalence relevant to your own clinical or research question? Factors Influencing Estimates of Prevalence Ideally, factors that might have a true causal relationship to the development of congenital cardiac disease and hence influence the true incidence should be identified Identification of such factors may allow for the prevention of congenital cardiac disease or provide new knowledge as to etiology and development The identification of these associations comes mainly from observational studies Environmental Factors The most widely held belief is that congenital cardiac disease is the product of an interaction between genetic and environmental factors However, evidence has yet to progress sufficiently far to prove this notion, although advances in the understanding of genetic underpinnings continue to increase For example, recent studies have suggested the presence of an interaction between maternal genes and maternal exposures to aromatic hydrocarbons and congenital heart disease.7 Numerous environmental factors have been linked to such development, independent of any already known genetic influence or predisposition.4 A scientific statement from the American Heart Association reviewed studies of prevalence and summarized studies of environmental factors.8 In Table 13.3, positive associations for maternal illnesses and maternal exposures are highlighted Table 13.3 Fetal Exposures and Increased Risk of Congenital Heart Defectsa Odds Ratio MATERNAL ILLNESS Phenylketonuria52–55 Pregestational diabetes56–59 Febrile illness56,60–62 Influenza62,63 Maternal rubella64 >6 3.1–18 1.8–2.9 2.1 b