What are the Most Common Chromosomal Abnormalities ?
Down syndrome is among the most common of these disorders, affecting about 1 in 800 to 1000 live-born babies. The risk of this and other trisomies increases with the mothers age. The risk of having a live-born baby with Down syndrome is about 1 in 1250 for a woman at age 25, 1 in 1000 at 30, 1 in 400 at 35, and 1 in 100 at age 40. The outlook for children with Down syndrome is far brighter than it once was. Most have mental retardation in the mild to moderate range. With early intervention and special education, many learn to read and write and participate in diverse childhood activities. (For more information, see Down syndrome fact sheet.) Babies also can be born with extra copies of chromosomes 13 or 18. These trisomies are usually much more severe than Down syndrome, but fortunately less common, each affecting about 1 in 5000 babies. Babies with trisomies 13 or 18 generally have severe mental retardation and many physical birth defects. Sadly, most affected babies die before their
