Definition - What does Binucleate Blastomere mean?
A binucleate blastomere is an abnormality of a cleavage-stage embryo in which embryonic cells have two haploid or two diploid nuclei of the same size. High incidence of such nuclear abnormality is related to low implantation and pregnancy rates, chromosomal abnormalities, and arrested embryo development.
Most specialists performing assisted reproduction would not choose to transfers embryos containing binucleate blastomere. In some cases, where no other embryos are available, a decision regarding the transfer of such embryos may be made on a case-to-case basis.
FertilitySmarts explains Binucleate Blastomere
Embryonic cells called blastomeres continue to divide through mitosis after fertilization of zygote. Mitosis results in the division of a cell into two daughter cells, each having one nucleus. Duplication of chromosomes occurs before division, and so each daughter cell has the same type and number of chromosomes as the parent cell. An error in this process could result in blastomeres having more than one nucleus, which could either be haploid (n = one complete set of chromosomes) or diploid (2n = two complete sets of chromosomes).
The specific cause of binucleate blastomere remains unclear, but the following factors are thought to contribute to this phenomena:
- Imperfect mitosis
- Damaged DNA
- Dysfunction of the mitotic spindle
- Alterations of the nuclear membrane
A nuclear membrane surrounds the nucleus of the cell and protects the DNA from cytoplasm present outside the nucleus. A modification in this nuclear membrane results in altered chromosomal distribution.
Additionally, an absence of cytokinesis (a division of cytoplasm at the end of mitosis or meiosis) after the occurrence of normal karyokinesis (a division of nucleus during mitosis) is also linked to binucleate blastomere formation.