Prenatal diagnosis of Down's syndrome: a method for measuring the consistency of women's decisions.

A method was developed for judging the quality of womens' decision making in the field of prenatal diagnosis by measuring the internal consistency of their replies to a series of hypothetical decisions. Seventy-three nonpregnant women were interviewed using a lottery technique to elicit the risks of the birth of a Down's child at which they would request the two main procedures for prenatal diagnosis, amniocentesis and chorionic villus biopsy (CVB). The consistency of their replies was tested by performing a third lottery to elicit at what CVB-related abortion risk the subject would choose CVB in preference to amniocentesis. Almost half the subjects were inconsistent, in that their difference level on this third lottery differed by a factor of two or more from that expected from the first two lotteries.