The practical importance of pedigree analysis in women considering invasive prenatal diagnosis for advanced maternal age or abnormal serum screening tests.

Genetic counselling prior to prenatal diagnosis subserves several functions, one of them to put the planned prenatal test into the wider context of the personal and familial medical history. Even though considered a pivotal part of counselling, little is known about the informational yield and practical relevance of a comprehensive pre-test pedigree analysis. This is particularly true for patients who do not consider prenatal diagnosis for a specific heritable disorder with a high recurrence risk in the ongoing pregnancy, but for a moderate risk for conditions such as Down syndrome that mostly arise de novo. We analysed the informational yield of pedigree analysis for such patients through a retrospective analysis of 1356 consecutive genetic counselling sessions. All cases were referred for advanced maternal age or an abnormal result upon triple serum marker screening. 148 cases (10.9%) were classified as having a significant and previously unknown genetic or teratologic risk factor for the fetus that was uncovered through pedigree analysis. Of these cases, 55% could be recommended a specific prenatal test covering the previously unknown genetic risk factor.