A case of apparently balanced de novo complex chromosome rearrangement with three breaks found in foetus by amniotic fluid examination is described. Amniocentesis was indicated because of low AFP in maternal serum during the first pregnancy of 25-year-old healthy woman. Her family anamnesis as well as her husbands on was insignificant, chromosomes were normal. Fetal karyotype was 46,XY,t(3;13;4)(q26.2;q21.3;q12). To eliminate further cryptic aberrations the multicolor FISH technique was employed. The risk of serious inborn malformation in complex rearrangement with three breaks was estimated on the basis of literary data to be 10.5 % (3.5 % per each break). The couple decided to terminate the pregnancy. No distinct anomaly was found in the fetus. Only 12 prenatal diagnoses of the complex balanced chromosome rearrangements formed de novo can be found in the literature. Total risk of the serious malformation relating to that small group of described cases is rather high. Only substantial enlargement of the clinic may enable to use prenatal evaluation of each individual case according to the number of chromosomal breaks or according to other criteria with more accurate results.

        Key words: prenatal diagnosis, complex chromosome rearrangements, translocation, de novo