Policies and practicalities impacting birth outcomes surveillance: A closer look at Down syndrome birth prevalence

Background.  Amniocentesis to diagnose Down syndrome has been a part of prenatal care for nearly 50 years.  In 2007, the American Congress of Obstetricians and Gynecologists recommended that clinicians offer all pregnant women testing for chromosomal abnormalities, including Down syndrome.  From a public health perspective, this policy marks a shift from a model of case detection based predominately upon age, personal, or family history towards a model of universal screening, regardless of risk.  With this health policy change, we might expect more patients than previously will receive screening results indicating a higher likelihood of a Down syndrome-affected pregnancy.

Purpose.  This systematic review investigates Down syndrome birth prevalence, as a proxy for incidence.

Methods.  PubMed was searched for peer-reviewed studies, identifying 2,105 articles.  Specific criteria were applied.  Using a form developed for this study, two independent reviewers extracted data about purpose, study design, sample demographics, case definition, and main outcomes related to Down syndrome birth prevalence.

Findings.  The pooled Down syndrome birth prevalence among the general population is 12.6 per 10,000 live births (9,368 cases/7,436,069).  Variation may be attributable to methodological approach, including differences in case ascertainment.

Conclusions.  Birth prevalence may be valuable to direct adequate and appropriate resources to live-born infants with Down syndrome and their families, but true incidence might be more informative.  Enacting policies to establish longitudinal, cohort studies of pregnant women may help to generate information that is a better proxy for incidence than birth prevalence and may improve evidence for maternal and child health program planning.