THE ROLE OF CORDOCENTESIS IN ASSESSMENT OF MOSAICISM FOUND IN AMNIOTIC-FLUID CELL-CULTURE

Chromosomal mosaicism presents one of the most difficult problems in p renatal cytogenetic diagnosis, requiring the differentiation of true m osaicism from pseudomosaicism. To overcome associated problems and to prevent termination of normal pregnancies, we investigated 23 pregnanc ies in which true mosaicism has been found in amniotic fluid cell cult ure. A fetal blood sample was obtained by cordocentesis for rapid kary otyping, and meticulous sonographic examinations were carried out for detecting fetal abnormalities. The 23 cases in which mosaicisms were f ound in amniocytes involved five cases with sex chromosomal abnormalit ies, twelve with autosomal trisomy, four with autosomal structural def ects, one with a supernumerary marker and one with tetraploidy. The ka ryotype from fetal leukocytes confirmed the diagnosis of mosaicism in only three out of 23 cases. These three included: two autosomal trisom ies (47,XY+13/47,XY+21 and 46,XY/47,XY+21) and one sex chromosome mosa icism (45,X/46,XY). These were all selected for elective termination o f pregnancies by the parents' request. Post abortion karyotype re-conf irmed previous karyotype. The other twenty lymphocyte karyotypes were normal, and of these, 19 patients gave birth at term, and one delivere d prematurely due to premature rupture of membranes. All 20 born infan ts were found normal by both neonatal examination and re-karyotypes. W e conclude that finding of mosaicism in amniotic fluid culture require s further investigation. Furthermore, in the presence of amniotic flui d cell true mosaicism and normal karyotype in fetal blood, continuatio n of the pregnancy is safe and to be recommended.