Many of us know someone who would desperately like to have a girl. Or a boy. Perhaps a couple has several children of one gender already and would like to have another child — but would only consider doing so if the 50/50 odds could be shifted in favor of the other gender. Or, perhaps a couple is seeking infertility treatment, a lready has one child, and would prefer that the next child is of the other gender. Yet another couple may want to avoid passing one of the more than 500 gender-linked genetic diseases to their child might consider using it.

When a sperm with a Y chromosome fertilizes an egg, it makes a boy. When an X chromosome bearing sperm fertilizes, it makes a girl. Any given sperm sample contains an even (50/50) amount of X (female) and Y (male) bearing sperm.

Couples have sought to influence the gender of their children for hundreds of years. In ancient Greece, men believed that lying on their right side during intercourse increased the likelihood of a male child. A Chinese birth calendar buried over 700 years ago in a tomb outside Beijing is said to predict gender by when conception occurred. In 18th century France, men would tie off their right testicle to ‘guarantee’ having a boy. In modern day America other methods have been tested such as timing of intercourse, sexual positions or placing live sperm on an albumin gradient. None of these methods has been shown to be scientifically valid. A proprietary flow cytometry method called Microsort was recently terminated after FDA review.

When couples decide that they want a method of gender selection that offers them an almost 100% chance of obtaining the desired gender, IVF with genetic testing of the embryos is the method of choice. In PGD, one to two cells are removed from these early embryos, and then DNA based genetics analysis is performed in highly-specialized laboratories. Upon completion of the analysis, which takes about 24 hours, couples can select which embryos they will use. If pregnancy results, there is almost a 100% chance it will be of the desired gender. This method is particularly helpful for couples where the risk of having a male child with an X-linked genetic disease is significant. The Ethics Committee of the American Society of Reproductive Medicine now considers family rebalancing as ethically acceptable.

Learn more Dr. Walid Saleh and CRE (previously SIRM-Dallas). Read other articles from Dr. Saleh on the ABC of infertility by clicking HERE.