OBJECTIVETo analyze sex chromosome mosaicisms in early cleavage-stage human embryos and blastocysts with poor embryo quality score based on the numbers of pronucleus(PN) zygotes using X,Y dual color fluorescence in situ hybridization (FISH), and to discuss the possible mechanisms.

METHODSFresh or frozen-thawed early cleavage-stage human embryos and blastocysts with poor embryo quality score not suitable for embryo transfer were studied with dual color FISH.

RESULTSDouble signal rate of 2PN among early cleavage-stage embryos was 66.67%, which was significantly higher than 1PN and 3PN embryos. Single signal rate of 1PN early cleavage-stage embryos was 90.41%, which was significantly higher than 2PN and 3PN ones. Three signal rate of 3PN early cleavage-stage embryos was 28.00%, which was significantly higher than 1PN and 2PN ones. Double signal rate of 3PN ones was 46.00%, which was significantly higher than 1PN ones. The polyploid rate of frozen-thawed early cleavage-stage embryos was 23.53%, which was slightly higher than that of fresh embryos, but with no statistical significance. The mosaicism rate of 24 blastocysts was 100.00% and the double signal dominant (≥ 50%) rate was 62.50%, which was significantly higher than the rate of early cleavage-stage embryos.

CONCLUSIONUsing 2PN as the criterion for embryo quality score cannot guarantee the selection of normal fertilized embryo for transplantation. Frozen-thawed embryos may harbor more polyploid cells. To avoid the selection of embryos with abnormal chromosomes, combinations of pre-implantation genetic diagnosis (PGD) and prenatal diagnosis are necessary. Meanwhile, blastocysts with poor quality scores may provide an important source for embryo stem cells.