To what extent would women prefer chorionic villus sampling to amniocentesis for prenatal diagnosis?

Sixty-six pregnant women and 46 doctors were interviewed about their preferences for chorionic villus sampling (CVS) or amniocentesis for prenatal diagnosis in a hypothetical situation where the indication was late maternal age. The standard gamble method was used to calculate each individual's degree of preference for one procedure over the other (utility) expressed in terms of the risk of miscarriage associated with the preferred procedure that would be tolerated in order to have that procedure. Utilities for each group were calculated and compared. Pregnant women nominated a median utility for CVS of a miscarriage rate of 0.9%, while doctors nominated a median utility for CVS of a miscarriage rate of 1.2%. The difference between these utilities was not statistically significant. The method described in this study can enable potential consumers of a new procedure to provide the minimum 'clinically important difference' between a new procedure and an existing procedure necessary for calculation of the sample size in a controlled clinical trial.