Diagnostic Genetic Testing
Diagnostic genetic testing in multiple gestations presents unique and unmatched challenges compared with singleton pregnancies. To accomplish genetic diagnoses prenatally, an invasive procedure such as first-trimester chorionic villus sampling or mid-trimester amniocentesis is necessary. Obtaining a sample of cells from each fetus in a multiple gestation is more complex and poses greater obstetric risks. Not only are two or more fetuses involved, but multiple gestations typically occur in older women who are at increased risk for aneuploidy. In addition, each fetus from a multiple gestation may also be at increased risk for congenital malformations compared with a singleton pregnancy. The genetic problems and counseling issues posed by multiple gestations are acutely dramatized in the case of the successful application of assisted reproductive technologies whereby the common practice of transferring two or more embryos increases the likelihood of multiple gestations1, previously infertile couples having become pregnant may now not only have to consider undergoing invasive genetic testing with all of its attendant risks including pregnancy loss, but also must be counseled concerning the unique ethical and moral issues engendered if only one fetus in a set of multiples is found to be genetically abnormal.