Discoveries and Data: Specific Conditions



Down syndrome—found in about 1 in 660 pregnancies in California—is the most common chromosome abnormality. An extra chromosome (trisomy 21) causes distinctive physical features, structural birth defects and mental retardation.

More than half of affected children have heart defects; many have other associated birth defects.

About 10% of babies with Down syndrome die before age 1. The average lifetime cost for medical treatment, educational services and lost productivity is $451,000.


As a woman gets older, her risk of having a pregnancy with Down syndrome increases. However, over half of Down syndrome infants are born to mothers under 35—although younger mothers have lower risk, they have more babies, therefore accounting for more affected births.

Racial/ethnic differences in Down syndrome rates are primarily due to the distribution of births by age. For example, Asians have a higher proportion of births to older mothers, increasing the rate of Down syndrome; Hispanics and Blacks have more births to younger mothers. ref_book-5101664


A variety of prenatal tests are available to detect Down syndrome.

bullet-5978574 Women over age 35 are routinely offered prenatal diagnosis with amniocentesis or chorionic villus sampling (CVS) because of their higher risk.
bullet-5978574 Blood tests during pregnancy can screen for higher or lower risk for Down syndrome based on the levels of various chemicals in the blood. Follow-up testing confirms whether a pregnancy is affected. California’s Expanded AFP screening, a prenatal blood test, can detect about 40%-66% of pregnancies with Down syndrome.
bullet-5978574 From 1989-91, California had a 26% reduction in livebirths with Down syndrome due to prenatal diagnosis and medically indicated pregnancy termination. A 49% reduction was seen for mothers over age 35, with a 7% reduction for mothers under 35. ref_book-5101664


Many Down syndrome conceptions result in miscarriage. Do pregnancy factors increase this miscarriage risk, thereby reducing the chance of having a recognized Down syndrome pregnancy? A study of 2000 mothers found:

bullet-5978574 Women with high alcohol consumption (more than 4 drinks/week) are less likely to have recognized Down syndrome pregnancies.
bullet-5978574 High coffee consumption (4 or more cups daily) also reduced risk of a recognized Down syndrome pregnancy. These mothers were about 50% more likely to have miscarried a previous preganacy compared to mothers who consumed less coffee.
bullet-5978574 Smoking did not alter risk. ref_book-5101664

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