Affiliated Physicians: Maternal Fetal Medicine
What are trisomies?
The term trisomy is used to describe the presence of three chromosomes, rather than the usual matched pair of chromosomes. For example, if a baby is born with three #21 chromosomes, rather than the usual pair, then the baby would be said to have "trisomy 21." Trisomy 21 is also known as Down syndrome. Other examples of trisomy include syndromes like trisomy 18 and trisomy 13. Again, trisomy 18 or trisomy 13 simply means the child has three copies of the #18 chromosome (or of the #13 chromosome) present in each cell of the body, rather than the usual pair.
What is Down syndrome?
Down syndrome is a genetic disorder that involves birth defects, intellectual disabilities, characteristic facial features. Additionally, it often involves heart defects, visual and hearing impairments, and other health problems. The severity of all of these problems varies greatly among affected individuals. Down syndrome is one of the most common genetic birth defects, affecting approximately one in about 800 babies. In this country, around 250,000 individuals have Down syndrome. Life expectancy among adults with Down syndrome is about 60 years, though average lifespan varies.
The term Down syndrome comes from Dr. Langdon Down, the doctor who first described the collection of physical symptoms in 1866. It was not until 1959 that the cause of Down syndrome (the presence of an extra #21 chromosome) was identified.
The vast majority of women have healthy pregnancies and their babies are born without difficulties. However, women with high-risk pregnancies often need a close watch for potential problems or complications. Fortunately, there are many tests and procedures to monitor the health of both mother and baby. Many of these pose little or no risk and can provide tremendous amounts of information to doctors, midwives, and expectant parents. Some types of testing and procedures, however, do carry some risks to mother, baby, or both.