Down Syndrome
Testing For Down Syndrome
Cytogenetic analysis looks at the number and structure of a person's chromosomes. This test, which can be performed on a blood sample, is the test used to definitively determine if an individual has Down syndrome.
Risk of Down syndrome and other chromosomal abnormalities increases with maternal age. Adapted from Evans, 1989.
| Maternal Age | Risk of Down Syndrome | Total Risk for all Chromosomal Abnormalities |
| 20 | 1/1667 | 1/526 |
| 21 | 1/1667 | 1/526 |
| 22 | 1/1429 | 1/500 |
| 23 | 1/1429 | 1/500 |
| 24 | 1/1250 | 1/476 |
| 25 | 1/1250 | 1/476 |
| 26 | 1/1176 | 1/476 |
| 27 | 1/1111 | 1/455 |
| 28 | 1/1053 | 1/435 |
| 29 | 1/1000 | 1/417 |
| 30 | 1/952 | 1/385 |
| 31 | 1/909 | 1/385 |
| 32 | 1/769 | 1/322 |
| 33 | 1/602 | 1/286 |
| 34 | 1/485 | 1/238 |
| 35 | 1/378 | 1/192 |
| 36 | 1/289 | 1/156 |
| 37 | 1/224 | 1/127 |
| 38 | 1/173 | 1/102 |
| 39 | 1/136 | 1/83 |
| 40 | 1/106 | 1/66 |
| 41 | 1/82 | 1/53 |
| 42 | 1/63 | 1/42 |
| 43 | 1/49 | 1/33 |
| 44 | 1/38 | 1/26 |
| 45 | 1/38 | 1/21 |
| 46 | 1/23 | 1/16 |
| 47 | 1/18 | 1/13 |
| 48 | 1/14 | 1/10 |
| 49 | 1/11 | 1/8 |
Prenatal diagnosis for Down syndrome (testing for the condition during pregnancy) is possible. Chromosome studies can be performed on fetal cells collected via chorionic villus sampling (CVS) at ten to twelve weeks of pregnancy or by amniocentesis at fifteen to twenty weeks of pregnancy. Because of the link between the mother's age and the chance of Down syndrome, prenatal diagnosis for Down syndrome and other chromosome conditions is routinely offered to women thirty-five and older. Whether to pursue prenatal diagnosis is a personal decision that can only be made by the parents.
SEE ALSO BIRTH DEFECTS; CHROMOSOMAL ABERRATIONS; MEIOSIS; MOSAICISM; NONDISJUNCTION; PRENATAL DIAGNOSIS.
Angela Trepanier
and Gerald L. Feldman
Bibliography
Evans, Mark I., et al. Fetal Diagnosis and Therapy: Science, Ethics, and the Law. Philadelphia, PA: JB Lippincott Co., 1989.
Gardner, R., J. McKinlay, and Grant R. Sutherland. Chromosome Abnormalities and Genetic Counseling, 2nd ed. New York: Oxford University Press, 1996.
Nussbaum, Robert L., Roderick R. McInnes, and Huntington F. Willard, eds. Thompson & Thompson Genetics in Medicine, 6th ed. Philadelphia, PA: W. B. Saunders, 2001.
Pueschel, Siegfried M., ed. A Parent's Guide to Down Syndrome: Toward a Brighter Future, 2nd ed. Baltimore, MD: Paul H. Brooks Publishing, 2001.
Internet Resource
Cohen, William I., ed. "Health Care Guidelines for Individuals with Down Syndrome: 1999 Revision." Down Syndrome Quarterly 4, no. 3 (1999): 1-15. <http://www.denison.edu/dsq/health99.shtml>.
Additional topics
Medicine EncyclopediaGenetics in Medicine - Part 1Down Syndrome - Clinical Features, Chromosomal Basis Of Down Syndrome, Testing For Down Syndrome