Direct Visualization of Metaphase-II Chromosomes in Human Oocytes Under an Inverted Microscope

Identification of Metaphase-II (M-II) chromosomes in living human oocytes is very important when performing intracytoplasmic sperm injection (ICSI) or nuclear transfer as has been reported in several studies and registered in some recent patents that we reviewed. However, until now studies of the M-II chromosomes have been substituted by studies of the M-II spindle because of lack of visualization of the M-II chromosomes. We developed a new method for the visualization of the M-II chromosomes that has a success rate above 90% without the use of any stains or optic devices. It is now possible to perform ICSI with a lower risk of damaging M-II chromosomes. This technique increases the potential for embryonic development resulting in a better clinical outcome, and is expected to contribute to the rescuing of the advance oocytes and mitochondrial disease following the nuclear transfer.