Abstract
On the basis of 480 prenatal diagnostic karyotype studies, carried out since 1971 in Zurich. the following types of problems were considered: (1) The difficulty is inherent in the counselling problem itself, as an unusual chromosome anomaly in a parent. (2) True fetal mosaicism. (3) Somatic mutations during culture. (4) Growth of maternal cells. In problems of type (1), it is known in advance that the prenatal diagnosis has limitations. Problems of the types (2) to (4) can be solved to some degree by using in situ preparations and the clone-wise analysis. In (2) and (3) analysis of 15 metaphases from 5 to 10 clones has been informative, somatic mutations usually being restricted to single cells within clones with otherwise normal karyotype. When entire clones exhibit a deviating karyotype, the proportion of abnormal to normal clones will help decide whether it is a case of (2) or (3). Also problem (4) is elucidated by the in situ method, since maternal cells. generally. differ in their growth pattern from fetal cells. If uncertainties persist, the comparison of fluorescent markers of presumed fetal cells to those of the mother is apt to resolve the problem. Somatic mutation and maternal cell growth should not be considered as a source of unavoidable pitfalls in prenatal cytogenetic diagnosis. By anticipating these events and by applying appropriate techniques. diagnostic errors can be kept at a very low level.
Schmid, Werner