GENDER SELECTION (SEX SELECTION)

Gender selection refers to the determination of the desired gender prior to implantation of the embryo. The odds of having a boy or a girl are almost 50/50 in a natural conception cycle and dependent on the sperm. The egg has 22 chromosomes plus the X chromosome, and the sperm brings another 22 chromosomes with either an X or a Y chromosome. If the sperm that fertilizes the egg has a Y chromosome, the end result is a boy and a girl if sperm contains the X chromosome.

Historically, gender selection was offered to patients with genetic diseases that are more common in one gender versus the other. X-linked disorders refer to diseases that are gender specific and can be limited with the process of gender selection. Family balancing on the other hand is a more recent and relatively common request for gender selection and rarely a person may request a specific gender without any medical necessity. Such cases have been challenging for fertility practices and there is still controversy in honoring such an elective request.

There are currently two options for gender selection and the first option is to identify and isolate the sperm that would result in the desired gender, and use the selected sperm to fertilize the egg (Sperm Sorting - Microsort). Alternatively, eggs can be fertilized with unselected sperm and the embryos can be tested genetically for the desired gender (Preimplantation Genetic Diagnosis – PGD).

Microsort technology allows the sperm to be sorted based on the presence of X or Y chromosomes with approximately 60-80% accuracy. Any given sperm sample contains an even (50/50) amount of X (female) and Y (male) bearing sperm. MicroSort uses a machine called a flow cytometer to sort sperm such that the sorted sperm population is enriched in either X (female) or Y (male) bearing sperm depending on the desired gender.

The separation of male and female sperm is based on the measurable difference in the quantity of genetic material (DNA) they contain. The sperm absorbs a dye, which attaches temporarily to the DNA, or genetic material, inside the individual sperm. When exposed to laser light, the dye fluoresces. Since the X chromosome is larger than the Y, there is more DNA for the dye to attach to and consequently, the sperm with the X chromosomes will fluoresce more brightly than those with Y chromosomes. The flow cytometer is able to pick up these differences in brightness and separate the sperm as they move through the machine one at a time. Although initial reported medical data suggested impressive results, further larger scale studies are still needed to confirm the applicability of this technology with good reliability.

Once the sperm has been sorted, it can be used with various assisted reproductive techniques to achieve a pregnancy. The most common method uses the sorted sperm with intrauterine insemination (IUI). In such a procedure, the woman is monitored carefully to establish the time of ovulation by the fertility specialist or through the use of ovulation predictor kits at home. Insemination is performed on the day of ovulation. On the day