[Genetic counselling (results of ten years experience). III. Evaluation of risk (author's transl)].

Among 924 consultations for definite or probable genetic disorders, two persons out of five seeking counselling run a high risk (10% or more) of having an affected child, one in five a risk varying between 1% and 9%, and two out of five a negligeable risk (less than 1%). In most cases (three out of four) individuals with affected relatives could be completely reassured, whilst one out of two affected persons seeking counselling ran a high risk of having a child who would suffer the same handicap. Among the normal parents with affected children, one out of three could be completely reassured, but on the other hand the same proportion ran a high risk of having another affected child. The calculated risks were compared in prenuptial, pre-pregnancy and prenatal counselling. The evaluation of the risk is only the first step in the counselling and certain special situations were chosen to demonstrate the factors which can modify the risk. The authors stress that genetic counselling, which is rarely simply indicative, should often be directive. In some cases, the prenatal diagnosis converts the theoretical risk into a certainty.