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Sex Selection

A good mind set for discussing sex selection is to examine a belief on sex selection that persisted for many years. People believed that boy sperm came from the right testicle and girl sperm came from the left. Tie off the left testicle and you would be assured of having a boy! There is rationality to this approach and it works about 50% of the time. Similarly reasonable approaches to sex selection have persisted to this day. Some of them use sexist assumptions about male and female sperm (some of us like to think that the boy sperm swim faster). Occasionally, a little bit of science is thrown in to make the explanation sound more rational. (X -bearing sperm have a greater mass than Y-bearing sperm.)

Many papers in the medical literature show a small statistical difference in the ratio of boys to girls related to simple fertility variables (fertilization of an older egg, use of clomid, use of HCG, etc.). However, these differences are very small (a few percent) and not really helpful to the couple who wants a girl after three boys.

There are three readily available techniques for sex selection available in the United States, which claim a high degree of effectiveness in sex selection. Two of these do work (and are available at Infertility Solutions).

Flow cytometry is a method of sorting cells utilizing fluorescent tags temporarily or permanently placed on the cells. IVF and Genetics Institute has developed a technique for sorting X (male) and Y (female) sperm using this technology. The use a flow cytometer specially adapted to work with sperm and a DNA stain on live sperm separates X- and Y- bearing sperm based on the amount of DNA in the sperm. Since there is only a 3% difference in the mass of an X- or Y-bearing sperm, this process is not very efficient and a relatively small number of sperm can be collected of one sex or the other. This sperm can then be used for either IUI or IVF. Given the small number of sperm produced, IVF (ICSI) is usually a more efficient way of using the specimen than IUI. This technique is best at producing female sperm and has a greater than 70% success in producing girl babies.

PGD is a technique in which a day 3 embryo is biopsied and stained for the presence or absence of a Y chromosome. Only embryos of the desired sex would be transferred to the patient with an expected success rate of 99% in producing boys or girls. Patients wanting this technique would have to undergo an IVF cycle in order to produce these embryos.

The third technique uses albumen gradients to separate sperm. There are several variations of this technique in use. DNA staining of the separated sperm does not support it being effective in separating the X- and Y-bearing sperm. The most widely used recipe for this technique is patented and to my knowledge has not been subjected to traditional unbiased scientific study. Theories behind why this is supposed to work do not appear to be supported by our understanding of sperm physiology. Physicians who use this technique should be pressed to justify its use.

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