The main aim of this study was prospective interphase FISH diagnosis of chromosomal anomalies in spontaneous abortion specimens. We used a probe set for chromosomes 1, 9, 13, 14, 16, 18, 21, 22, X, and Y, as it well known that aneuploidies involving these chromosomes are most frequent in humans [1,2,8,9]. The results obtained allowed us to explain the cause of fetus losses in 55% of the speci­mens analyzed. The presence of chromosomal aneuploi­dies involving other chromosomes (2, 3, 4, 5, 6, 7, 8, 10, 11, 12, 15, 17, 19, 20) cannot be excluded as we have not tested for these by FISH in the present study. In recent studies, chromosome 2, 7, 10, 15, and 17 are also recog­nized as being involved in spontaneous abortions [3,8]. Therefore, the frequency of chromosomal abnormalities in these specimens could be higher. The set of DNA probes used is highly informative for aneuploidy screening in spontaneous abortion specimens. Recently, Jobanputra et al. [8], using interphase FISH with a probe set for chromo­somes 13, 15, 16, 18, 21, 22, X and Y, have identified 54% of chromosomal abnormalities in spontaneous abor­tion specimens, which is similar to data obtained in the present study.

Fluorescent in situ hybridization that allows the study of aneuploidies in a large number of interphase cells could be considered as an efficient method for analysis of chro­mosomal mosaicism. Accurate scoring of a large number of interphase nuclei using two- or three-color FISH per­formed in our study, allowed us to identify mosaic forms of aneuploidies and polyploidy in 20 (51.3%) specimens with chromosomal abnormalities. Therefore, postzygotic non disjunction of chromosomes could take place in fe­tuses during the first trimester of pregnancy with a higher frequency than has been detected before using karyotyping techniques.

There are several reports about an excess of normal female karyotypes over normal male karyotypes in sponta­neous abortion specimens [7,8]. In the present study we detected 24 normal female and four normal male karyo­types among the 63 specimens analyzed. A prevalence of female fetuses (male/female ratio 15/48) was also detected among all the specimens studied. One can propose that contamination by maternal cells could occur during speci­men processing for FISH. Alternatively, the dramatic loss of male fetuses with chromosome abnormalities or lethal X-linked gene mutations, can take place in earlier stages of pregnancy thus leading to such a prevalence of female fetuses. The future direction of the study is to clarify the real cause of non random sex ratios.

The set of original DNA probes was found to be appli­cable for accurate and rapid screening of aneuploidies in spontaneous abortion specimens, allowing the determina­tion of regular as well as mosaic forms of chromosome abnormalities.