Gender Selection

There are many reasons why a couple would desire to select the gender of their future offspring. Some couples may have a personal preference for a specific gender, may desire to balance their family with children of both genders, or may desire to avoid a sex-linked genetic disease.

The sex of a child depends upon whether fertilization of the egg (which contains an X chromosome) occurs with a sperm containing an X or a Y chromosome. An XX embryo will become a female baby and a XY embryo will become a male baby.

Attempts to influence this process have been practiced as long ago as Ancient Greece. A number of publications in the lay press have purported to help parents determine the sex of their future offspring. Diet and timed intercourse are the two most common methods, but neither is effective.

The Preconception Gender Diet is based on the theory that a couple can improve their chances of having a female baby by increasing dietary intake of both calcium and magnesium. To improve chances of having a male offspring, increasing dietary intake of sodium and potassium have been purported to work. Follow-up studies have not been able to verify these claims.

Timing intercourse for gender selection is based upon the belief that X-bearing sperm live longer than Y-bearing sperm and that Y-bearing sperm swim faster than X-bearing sperm. However, studies which have attempted to correlate the sex of offspring with timing of intercourse have reported conflicting results. There is no strong evidence that timing plays an influential role in gender selection.

Scientific techniques used to select gender have focused on preconception gender selection, which utilizes techniques for sperm separation prior to fertilization, and preimplantation genetic diagnosis (PGD), which selects the desired gender after fertilization and prior to implantation.

Preconception gender selection utilizes the process of sperm separation, whereby semen is separated into X-bearing and Y-bearing sperm. A sperm sample with a higher percentage of the desired gender is used for fertilization by intrauterine insemination or in vitro fertilization (IVF). Separation of sperm can be accomplished through a variety of techniques that rely on well-established principles regarding human spermatozoa. These techniques include the swim-up separation method, albumin, and density gradients. However, the techniques purported to separate sperm by gender, although promising, have not found to be as reliable as initially reported when genetic testing was used to determine the Y- and X-bearing sperm concentrations of the separated fractions.

The only sperm-sorting technique that has had consistent genetically proven success in sorting sperm by gender is flow cytometry. In flow cytometry, sperm are sorted by gender based upon the amount of genetic material each sperm carries. Human X-bearing sperm are 2.8 percent heavier than Y-bearing sperm. In flow cytometry, sperm is coated with a nontoxic fluorescent dye that binds to the outside of the DNA of the sperm. Ultraviolet (UV) beams are passed across the dyed spermatozoa to excite the dye. The spermatozoa containing more genetic material (the X-bearing sperm) will have increased fluorescent intensity and be recognized by a fluorescence detector and then be sorted to separate the X- and Y-bearing sperm.

A large amount of sperm is lost in this sorting process. It is not unusual to end up with 100,000 motile sperm from a sample that originally contained more than 50 million motile sperm. Therefore, flow cytometry is appropriate only for those couples where the male partner has a normal sperm count. Either intrauterine insemination or preferably IVF is required due to the low final sperm counts and the fact that the sample is often frozen after the sort is performed. Although flow cytometry appears to be safe, more long-term data are needed to confirm efficacy.

Preimplanation genetic diagnosis (PGD) refers to the post-IVF biopsy of an embryo on day 3 in the lab, where genetic analysis is performed before the embryo is implanted. PGD can be used for gender selection by identifying the embryo's karyotype (the chromosomal characteristic of a cell) as male or female using rapid genetic testing completed within 48 hours to allow for transfer of embryos at or before the blastocyst stage. PGD is very expensive, and can only be offered in conjunction with IVF.

Sperm separation techniques can be used in conjunction with PGD to increase the number of embryos of a particular sex. It is still unclear how PGD may impact embryonic development following the removal of a blastomere (a cell produced during the cleavage of a fertilized egg), but there do not appear to be any long-term side effects to the offspring.

Gender selection is an ethically charged issue. Should anyone be able to choose the sex of their children? Should anyone have access to the reproductive techniques that can assist in selecting the gender of a child? Those who oppose the use of sex selection believe it could reinforce gender biases or lead to sex ratio imbalances, which is more relevant in countries where large sex-ratio imbalances already exist.

And what is the potential psychological harm done to children, regardless of whether they are the desired or undesired sex? These are important issues that remain unresolved.

Here at USC Fertility, we do help couples with gender selection. We strive to help our patients make informed choices—with medical and psychological assistance as necessary—as they decide what are the best choices for them as a couple or a family. Every situation involving gender selection is different and requires the personalized attention that we here a USC Fertility believe we can provide to our patients.