TREATMENT-RELATED CHROMOSOME-ABNORMALITIES IN HUMAN EMBRYOS

Mosaicism was studied in good quality embryos from four different cent res in order to assess the effects of follicular induction and exposur e to laboratory conditions on chromosomal status. The donated embryos were fully biopsied and analysed by fluorescence in-situ hybridization using probes for chromosomes X, Y, 13, 18 and 21, simultaneously. The number of abnormal cells present indicated the division at which mosa icism first occurred (4/4 cells at first division, 2/4 cells at second , 2/8 at third). The rate of mosaicism in embryos from different centr es varied greatly (P < 0.001). Most of the mosaic embryos were obtaine d before 1991. In one clinic increased mosaicism was found in embryos obtained before 1991 when compared to embryos obtained thereafter, The results suggest that certain culture conditions and/or hormonal stimu lation protocols may induce chromosomal abnormalities and partly expla in differences in pregnancy rates between in-vitro fertilization centr es.