Calculated risk of chromosomal abnormalities in twin gestations.

Publication/Presentation Date

12-1-1990

Abstract

Genetic counseling concerning the risks of chromosomal abnormalities in twin gestations can be difficult; the risk of amniocentesis is weighed against that of chromosomal abnormalities in either one or both of the twins. Because most twins are dizygotic (each with a risk a priori of aneuploidy), the chance that one of the fetuses is affected is greater than would be expected for a singleton. Only three possibilities would result in either one or both twin's being affected: 1) dizygotic twins with one fetus affected, 2) dizygotic twins with both fetuses affected, and 3) monozygotic twins with both fetuses affected. Using existing tables of estimated risks of chromosomal abnormalities in singleton gestations and mathematically derived formulas, we created tables defining the age-related risks of chromosomal abnormalities in twin gestations. According to these tables, a patient at 33 years of age with a twin gestation has a risk of Down syndrome in at least one of her twins equivalent to that of a 35-year-old with a singleton. Prenatal genetic testing should be considered for women with twins at a younger age than the traditional 35.

Volume

76

Issue

6

First Page

1037

Last Page

1041

ISSN

0029-7844

Disciplines

Medicine and Health Sciences

PubMedID

2146537

Department(s)

Department of Obstetrics and Gynecology

Document Type

Article

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