Estimating the Prevalence of Fetal Alcohol Syndrome a summary

Alcohol Research & Health,  Fall, 2001  by Philip A. May,  J. Phillip Gossage

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Since the late 1970s, many studies have reported on the prevalence of fetal alcohol syndrome (FAS), alcohol-related birth defects (ARBD), and alcohol-related neurodevelopmental disorders (ARND). The three main types of research methods used in these studies are passive surveillance, clinic-based studies, and active case ascertainment. This article describes each of these methods, including their strengths and weaknesses, and summarizes the estimated prevalence of FAS produced by each of these approaches. The maternal risk factors associated with FAS and other alcohol-related anomalies include advanced maternal age, low socioeconomic status, frequent binge drinking, family and friends with drinking problems, and poor social and psychological indicators. Overall, the available literature points to a prevalence rate of FAS of 0.5 to 2 cases per 1,000 births in the United States during the 1980s and 1990s. KEY WORDS: fetal alcohol syndrome; prevalence; epidemiological indicators; alcohol-related neurodevelopmenta l disorder; birth defects; statistical estimation; data collection; clinical aspects; population dynamics; risk factors; research in practice; research quality

Establishing the prevalence (1) and other epidemiological characteristics of fetal alcohol syndrome (FAS), alcohol-related birth defects (ARBD), and alcohol-related neurodevelopmental disorder (ARND) (2) has been a difficult challenge ever since Jones and colleagues (Jones and Smith 1973; Jones et al. 1973) described the first cases of FAS. Researchers have been constantly challenged by issues related to case finding, sampling, diagnostic criteria, and the coordination of interdisciplinary activities. Although the diagnostic features of FAS are generally well established, the specific assessment techniques used to make the definitive diagnosis are still matters of debate. Furthermore, the criteria for ARBD and ARND (formerly referred to as fetal alcohol effects [FAE]) remain even more in question today (Stratton et al. 1996; Aase 1994; Aase et al. 1995; Astley and Clarren 2000). Because of questions of assessment methods and difficulties associated with access to cases, studies that have attempted to determin e the prevalence of FAS, ARBD, and ARND are limited in number, vary widely in their methodology, and may leave the typical reader puzzled about the true pattern and the frequency of occurrence of these disorders.

This article will summarize the common methods used to study the prevalence and other epidemiological characteristics of FAS in the United States and review both similar and unique findings that have emerged in the literature from other countries. For each method, we present a survey of the studies conducted and summarize the research findings. We will highlight the biases, strengths, weaknesses, and key findings produced by each approach, and discuss the different populations studied.

THREE COMMON APPROACHES TO THE EPIDEMIOLOGICAL STUDY OF FAS

Researchers used three main approaches to study the prevalence and patterns of occurrence of FAS, ARBD, and ARND: passive systems, clinic-based studies, and active case ascertainment approaches. Of these three approaches, clinic-based studies are the most common, followed by passive systems, and then active case ascertainment. Passive systems are generally the least expensive, followed by clinic-based studies; active case ascertainment studies are frequently the most costly and time intensive (Stratton et al. 1996).

Passive Surveillance Systems

Researchers using passive systems to study FAS epidemiology use existing record collections in a particular geographical catchment area (e.g., a town or state). Researchers must first establish the criteria for defining a diagnosis of FAS, ARBD, or ARND, and then a ream of reviewers looks for documented or probable cases of children born with FAS and diagnosed in a particular time period. Three types of records are generally reviewed: birth certificates, special registries for children with developmental disabilities or birth defects, and/or the medical charts of hospitals and physicians. The Centers for Disease Control and Prevention (CDC) maintains the Birth Defect Monitoring Program (BDMP) in hospitals throughout the United States, tracking most major anomalies that occur at birth, including FAS (Chavez et al. 1988). Many recent passive surveillance studies have used multiple types of records to identify as many cases of alcohol-related anomalies as possible, since a case of FAS is frequently documented in more than one place (e.g., physician records, school records, and birth certificates) over time. These multiple records approaches are referred to as capture-recapture methods (Egeland et al. 1998).

The major advantage of passive methods is that they efficiently utilize existing health care systems, programs, and records that are already funded by other sources. This approach is therefore relatively inexpensive and easier to undertake than some other research methods. But there are also major disadvantages. Some birth defects, such as severe spina bifida and Down's syndrome, are easy to recognize and diagnose because the anatomical or genetic markers are obvious and well known to most obstetricians and pediatricians. FAS, ARBD, and ARND, however, are complex, involving multiple indicators of physiology, development, and behavior, many of which are not obvious at all or are at least more difficult to identify at particular ages (e.g., birth) (see Little et al. 1990; Aase 1994; Clarren et al. 2001). Therefore, passive systems, which generally depend on the diagnoses of many hundreds of non-specialist physicians, educators, and other service providers (who may miss FAS symptoms because of the circumstances of examination or the age at which the child is presented), lack the rigor and consistency of diagnoses that characterize other systems. Furthermore, passive systems depend on a variety of registries for complete and consistent records and are therefore vulnerable to the many contingencies that affect the quality of data in institutions where these data are collected.