Risk estimates for balanced reciprocal translocation carriers--prenatal diagnosis experience.

An analysis was performed on 40 families at risk for an unbalanced rearrangement in the fetus because one of the parents is a reciprocal translocation carrier. The overall risk at second trimester prenatal diagnosis was 14% (8/57). The individual risk for unbalanced offspring at second trimester prenatal diagnoses and at birth were estimated using empirical data by Stengel-Rutkowski et al. (1988). The risks at birth ranged from 0%-21.6%. Most reciprocal translocations (22 or 55%) were at low risk. Without risk (7 or 17.5%), medium risk (6 or 15%) and high risk (5 or 12.5%) translocations were about equally represented and relatively infrequent. The analysis shows that the mode of ascertainment as well as the measurement of lengths of observed or probable imbalances cannot serve as a reliable risk predictor in individual counselling. In the translocations ascertained through spontaneous abortions the risk is frequently small or nonexistent, but remarkable exceptions to this rule are observed. Translocations discovered through unbalanced offspring were found to belong to different risk groups with the exception of the no risk group. Individual risk estimates have to be performed as a basis of genetic counselling before or during pregnancy so that parents with reciprocal translocations can make their choices regarding the available options.