B. Rosenbusch et al., Cytogenetic analysis of human zygotes displaying three pronuclei and one polar body after intracytoplasmic sperm injection, HUM REPR, 16(11), 2001, pp. 2362-2367
BACKGROUND: Digynic zygotes with three pronuclei and one polar body obtaine
d after intracytoplasmic sperm injection (ICSI) were studied cytogeneticall
y to elucidate the frequency and origin of chromosomal abnormalities at the
earliest stage of conception. METHODS: Uncleaved, single-cell zygotes were
incubated with podophyllotoxin and vinblastine and fixed by a gradual fixa
tion air drying method. The chromosomes were stained with Giemsa. RESULTS:
Twenty-two (50%) out of 44 informative zygotes revealed cytogenetic alterat
ions, including aneuploidy (six cells, 13.6%), structural aberrations (10 c
ells, 22.7%) and combinations of numerical and structural abnormalities (tw
o cells, 4.5%). In one case (2.3%), double aneuploidy or an effect of chrom
osomal translocation could not be distinguished and one zygote (2.3%) turne
d out tetraploid due to injection of a diploid spermatozoon. Two zygotes (4
.5%) showed an irregular chromatid segregation between the two maternal com
plements. In completely analysable cells, the sex chromosome ratio XXX:XXY
was 17:15. CONCLUSIONS: Digynic ICSI zygotes carry a high rate of cytogenet
ic abnormalities that obviously have been transmitted by the participating
oocytes and spermatozoa. We also confirmed the previously reported, possibl
y ICSI-induced irregular oocyte chromatid segregation. The results suggest
that aneuploidy in the oocytes must have been caused by predivision instead
of non-disjunction.