Analysis of mosaic states in amniotic fluid using the in-situ colony technique.

Appropriate counselling and clinical management of the pregnant woman with a mosaic amniotic fluid cell karyotype are difficult. The majority of the data on mosaicism and pseudomosaicism are derived from studies employing the flask technique for the analysis of amniotic fluid cell cultures. Since the majority of laboratories now utilize the in-situ technique, such data may not be relevant when analyzing results from the in-situ colony technique. We reviewed the incidence of mosaicism in 6339 amniotic fluid samples using the in-situ technique. Data are presented on the types of aberrations and clinical outcomes. A classification of mosaicism is presented that distinguishes mosaicism of clinical importance from that which is obviously of extrafetal origin or artifactual. This approach clarifies the significance of mosaic states detected by the in-situ colony technique and provides a rational foundation for genetic counselling and for planning clinical interventions.