Detection of mosaic and non-mosaic chromosome abnormalities in 6- to 8-day old human blastocysts.

A reliable technique has been developed for the production of good quality G-banded chromosome preparations from 6- to 8-day-old human blastocysts (20-800 cell stage) from an in vitro fertilization programme. The technique involves a thymidine cell division synchronization step to reduce the exposure time to colcemid, in conjunction with a simple 70% acetic acid disaggregation procedure to produce discrete metaphases for analysis. Of 105 blastocysts processed by this technique, 9 were lost during handling and 10 showed no dividing cells. The remaining 86 produced useful separate metaphases with a mean mitotic activity of 6.5%. A full G-banded karyotype was obtained from 1-6 cells in 55 blastocysts (64%), incomplete G-banded analysis but with full information of ploidy was obtained from 18 blastocysts (21%), with 13 (15%) producing no useful cytogenetic results. Abnormalities observed included polyploidy, diploid/polyploid mosaicism, non-mosaic trisomy 16 (2 cases), 46,Xdel(X)-(q21)/46,XX (1 case) and several single cells with trisomies or structural anomalies in otherwise normal blastocysts. Variable levels of structural chromosome damage, with apparent interchanges, chromosome branching and anomalous chromatid pairing were also seen.