The sex of a child is determined at fertilization by the particular sperm which penetrates the egg: sperm cells carrying an X chromosome result in a female and those carrying a Y chromosome result in a male. Currently there is only one approach to gender prediction for family balancing: embryo biopsy with genetic testing (PGD) after fertilization in vitro (IVF). The MicroSort technique is no longer available for family balancing, and can be used only for sex-linked genetic disorders on an experimental basis.
Gender Determination through PGD
This technique detects the gender of early embryos after fertilization has already occurred through IVF. Embryos exhibiting normal development undergo biopsy with removal of one or more cells. The removed cells are analysed for chromosomal content before select embryos are placed in the uterus. The embryo biopsy is most commonly performed 3 days after fertilization then fresh embryos are transferred on day 5 or 6. Alternatively, the biopsy is done on day 5 embryos known as blastocysts which are then cryo-preserved for frozen embryo transfer in a subsequent cycle.
Chromosome analysis can reveal both the gender of each embryo and many abnormalities in chromosome number (aneuploidy). Aneuploidy is a major cause of miscarriages and accounts for genetic defects compatible with a live birth, such as Down’s and Turner syndromes. Genetic counseling is required to provide full understanding of the strengths and limitations of this invasive technique and the specific findings in each case. The accuracy of gender prediction by PGD is greater that 95% but it falls short of 100%.
For additional information about the IVF process (IVF Primer) and pre-implantation genetic diagnosis (PGD) click on the above links. The likelihood of achieving a live birth through IVF and PGD depends on such factors as the age of the woman providing the eggs, her ovarian reserve and uterus. However, there is no assurance that either a live birth or a child of desired gender will be achieved through this technique.
MicroSort® Sex Pre-selection for Genetic Diseases
Semen contains approximately 50% female and 50% male sperm cells. People have tried to change the sex ratio of children for millennia but the natural balance of 50:50 is not readily altered. Couples seek sex pre-selection either because of a genetic disease affecting one sex or for family balancing. Most of the older techniques for sperm selection, including albumin and density gradient centrifugation, have never been scientifically validated by reliable studies. The only technique which has been rigorously studied and found to be effective is flow cytometry patented as MicroSort®. The MicroSort® technology is based on the fact that the X chromosome is slightly larger than the Y chromosome. This slight difference in DNA content can be measured and used to separate the X- and Y-bearing sperm cells.
MicroSort sperm pre-selection works better for X-bearing sperm than for Y-bearing sperm. The technique has resulted in births of about 94% females with sorting for X-bearing sperm compared to only about 74% males with sorting for Y-bearing sperm. An excellent sperm count and motility are required with more than 100 million moving sperm per ejaculate. Currently only two locations offer MicroSort sperm processing, one laboratory is in Virginia and one in Southern California.
At present MicroSort is available only to avoid genetic defects. For further information, please consult the MicroSort website (http://microsort.net) or contact one of the MicroSort facilities by calling 1-866-472-4483 or 1-800-277-6607.