Down syndrome occurs in people of all races and economic levels. One in every 691 babies in the United States is born with Down syndrome, making it the most common genetic condition. Down syndrome occurs when an individual has a full or partial extra copy of chromosome 21. This additional genetic material alters fetal development and causes the characteristics associated with Down syndrome like low muscle tone, small stature, an upward slant to the eyes, and a single deep crease across the center of the palm.
The cause of the extra full or partial chromosome is unknown, but maternal age is linked to an increased chance of having a baby with Down syndrome. A 35 year old woman has about a one in 350 chance of conceiving a child with Down syndrome, and this chance increases gradually to 1 in 100 by age 40. At age 45 the incidence becomes approximately 1 in 30. However, due to higher birth rates in younger women, 80% of children with Down syndrome are born to women under 35 years of age.
Genetic counseling, prenatal screenings and diagnostic testing for parents is becoming increasingly important and can provide a definitive diagnosis with almost 100% accuracy.
Most screening tests involve a blood test and an ultrasound (sonogram), and are used to estimate the chance of having a child with Down syndrome. New advanced prenatal screens are able to detect chromosomal material from the fetus and provide a high accuracy rate. Other diagnostic tests include chorionic villus sampling (CVS) and amniocentesis. These procedures, which carry up to a 1% risk of causing a spontaneous termination (miscarriage), are nearly 100% accurate in diagnosing Down syndrome. Amniocentesis is usually performed in the second trimester between 15 and 20 weeks of gestation, CVS in the first trimester between 9 and 14 weeks.
You can find more information on Down Syndrome, as well as support here.
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