Nomograms to help inform women considering Down's syndrome screening

Objective: To derive graphical information for use in counselling women considering whether or not to have maternal serum screening for Down's syndrome. Design: Statistical modelling of the frequency distribution of estimated Down's syndrome risk for four marker combinations. Results: Nomograms are provided showing for each maternal age: (a) the detection and false-positive rates, and (b) the proportion of pregnancies with different estimated risks. Conclusion: When screening is offered, clinicians need to have information readily available on test accuracy and the likely result, which is specific to the individual.