Twin pregnancy with discordancy for Down's syndrome.

A twin pregnancy is described in which discordancy for Down's syndrome was diagnosed prenatally by karyotyping amniotic fluid cultures from each of the 2 sacs. The advantages of ultrasonography prior to genetic amniocentesis are discussed from this perspective. The observation that parents may deal in various ways with the reality of this prenatal dilemma demands an open-minded approach from obstetricians and genetic counselors.