Down's syndrome. Recent trends in the United States

Area of Science:

• Reproductive epidemiology
• Genetics
• Public health

Background:

• Down's syndrome (DS) incidence in the US is approximately 1/1,000 births.
• Maternal age is a significant factor in DS risk.
• Changes in maternal age distribution have impacted DS birth rates.

Purpose of the Study:

• To analyze trends in Down's syndrome incidence.
• To evaluate the impact of maternal age and prenatal diagnosis on DS rates.
• To project future DS birth distributions.

Main Methods:

• Analysis of crude incidence rates of Down's syndrome.
• Epidemiologic studies on maternal age and DS risk.
• Modeling of prenatal diagnosis impact.

Main Results:

• A reduction in births to women 35+ has halved DS births to this group.
• Crude DS incidence dropped from 1.33/1,000 in 1960 to 0.99/1,000 in 1978.
• Prenatal diagnosis in women 35+ may decrease overall DS incidence by only 20%.

Conclusions:

• Despite prenatal diagnosis, most Down's syndrome births (over 80%) will occur to younger mothers.
• Shifting maternal age distribution is a key driver of DS incidence trends.
• Targeted prenatal screening for older mothers has limited impact on overall DS rates.