Factors affecting the incidence of Down syndrome live births in Illinois from 1989 to 1997

Abstract

Purpose: Prenatal screening and elective termination are known to reduce the overall incidence of Down syndrome births. To evaluate socioeconomic and other factors that also have effects on incidence, through their association with screening and termination, all live births in Illinois between 1989 and 1997 were studied.Methods: Data sources consisted of the Illinois Adverse Pregnancy Outcomes Reporting System (a birth defect registry), statewide birth master files, and United States census data. There were 1,589,125 births evaluated in this study, including 1,747 Down syndrome cases. Logistic regression was performed to model Down syndrome births by maternal age, race, prenatal care, maternal education, urban or rural location of residence, trends over time, per capita income, and other variables.Results: The odds ratios (OR) were significantly increased for maternal age (for all women OR = 1.05 per year; 95% Cl = 1.03-1.07; and for women older than 35 a further OR = 1.01 per year; 95% Cl = 1.01-1.02). Increased risk was also found for whites(OR = 1.28; 95% C1 = 1.12-1.46), Protective effects were found for prenatal care (OR = 0.97 per visit; 95% Cl = 0.96-0.99), education (OR = 0.95 for each year of education attained; 95% Cl = 0.94-0.97), and urban residence (OR = 0.82; 95% Cl = 0.74-0.90). Over time there was a general protective effect (OR = 0.96 for each quarter; 95% Cl = 0.94-0.98). A slight protective effect was found for women over 35 living in higher per capita income areas (OR = 0.99 per year of age; Cl = 0.99-1.00).Conclusion: Variables associated with higher socioeconomic status and urban residence correlated with lower rates of Down syndrome live births. The findings are consistent with studies of usage patterns of prenatal diagnosis and have implications regarding the care provided to women in different socioeconomic circumstances.