1996] presented a case-control study in this journal, covering a total of 13 cases of limb deficiencies divided into 2 populations after chorionic villus sampling (CVS), namely the US Multistate CVS study and the Italian Multicentric Birth Defects study (IPMC). They pointed out that differences in results of various studies on this issue might be a consequence of different classification systems for limb defects. Classification and terminology of limb deficiencies is a crucial point in the discussion of a possible relationship between limb defects and first trimester prenatal diagnosis by CVS. Solving this communication difficulty might indeed help us get a step further in this ongoing and sometimes unproductive controversy.
Important differences in the use of terminology were mentioned by Froster and Jackson [1994] at the ASHG meeting in relation to the US Multistate CVS study, to which Botto et al. 119961 refer in their paper. Being directly addressed and realizing that the essential differences in classification systems were again missed by the authors [Botto et al., 19961 prompted me to delineate these differences in various classification systems which are presently in use for the description of congenital limb deficiencies, including the classification system we had used for analysing limb defect cases in British Columbia [Froster-Iskenius and Baird, 19921 and in the WHO-CVS study [Froster and Jackson, 19961. It might be important to emphasize that I do not claim that the system we use is any better than any other system for the classification of limb defects, but we had used this system consistently for the 2 large studies mentioned above and we think that if data from other authors are compared to data from our studies, there is a need for consistency in the use of definitions.
Classification of Congenital Limb Defects
There is agreement that "reduction" defects of the limbs are understood as defects in which skeletal parts