Gender selection

April 7, 2011Carole 1 Comment »

Preferring a child of one gender or another is as old as sex itself. Old wives tales abound of various methods to ensure that your child is a boy (or a girl).  For prospective parents, determining your child’s gender was believed to be dependent on what you ate, what you drank, what positions you used for intercourse or when during the lunar calender you had sex. The bottom line is that the sperm that carries an X chromosome will produce a girl child and the sperm that carries a Y chromosome will produce a boy child. There is no scientific evidence that any of the old wives tales hold any merit. All things being equal, every sex act resulting in pregnancy has a 50:50 chance of producing a boy (or girl).

Because the sperm determines the gender, there have been a variety of sperm selection methods proposed to enhance the chances that sperm carrying either an X or Y are favored.  Some are based on the idea that sperm carrying an X chromosome should be infinitesimally heavier than sperm carrying the smaller Y chromosome. Theoretically,  X and Y bearing sperm can be differentiated in the lab by various filtering methods.  For instance, in the Ericsson method, (described in more detail on the gender selection blog Ingender),  sperm are filtered over an albumin gradient to separate heavier and lighter sperm. This site is also a good resource for published articles if you want more information about gender selection methods. Proponents of the various spinning methods claim success rates of around 70% but frankly, rock solid scientific evidence is lacking to suggest that these methods are able to push gender selection outcomes away from 50% for either gender.

Intercourse timing schemes like the Shettles method or Whelan method suggest that timing intercourse either well in advance of ovulation or just before ovulation will have an impact on whether a boy or girl is conceived because whether the sperm carries a Y or X chromosome is supposed to have an effect on its longevity in the female body. Ironically, each of these methods argues for the opposite timing to produce a boy (or girl), suggesting again that neither method probably changes the outcome from the 50:50 chance. Critics of these various gender selection schemes suggest that these methods are most effective, not for sperm separation, but rather for separating patients from their money.

The only sperm selection method that has strong scientific merit is sperm sorting which employ labeling of sperm sex chromosomes with fluorescent dyes and literally sorting them into X and  Y bearing sperm using a high speed laser. This method has been trademarked as Microsort when used for human sperm selection. Microsort technology is currently under investigation in various fertility clinics under the auspices of FDA clinical trials investigating this as an experimental clinical method for humans. First invented by Larry Johnson, PhD at the USDA and later patented by the USDA, this method, widely used for sperm sorting in cattle and swine production is called the Beltsville Sperm Sexing Technology when applied to animal. In the late eighties, I heard Dr. Johnson give a fascinating lecture at Penn State (where I performed my graduate research studies in cattle reproduction) in which he described his new laser sperm sorting technique.  His flow-cytometry method of sperm sorting is scientifically based and can enrich the sperm population of either X or Y bearing sperm to approximately 90%. Notice, 90% is not 100% so patients aren’t guaranteed that they will achieve a pregnancy of the gender they desire. Still, this method is an advance over other methods because it is scientifically based with a wealth of efficacy data collected in the domesticated animal industry.  Any selection method will reduce the total number of sperm so depending on the total sperm number in the original ejaculate, these methods may not always leave enough sperm for insemination purposes, but certainly enough should remain post-sorting for use with either IVF or intracytoplasmic sperm injection (ICSI).

From time to time, patients have asked whether their embryologist can pick out a X- bearing or Y- bearing sperm just by looking at it when they select a sperm for sperm injection. Because some of the sperm selection methods that are advertised are based on  the swimming speed of sperm, I suppose it’s not unreasonable to ask the question, “Can embryologists pick out the heavier, possibly slower swimming sperm for injection to produce a girl embryo or select faster, presumably lighter sperm to produce boy embryos?”  The short answer is, “No, embryologists can’t tell the gender producing capabilities of a sperm by looking at either the shape or speed of the sperm”. If we could, it sure would save some time, money and ethical objections associated with gender selection.

If you want the potential for 100% accuracy in gender selection, the only option approaching 100% effectiveness is preimplantation genetic diagnosis (PGD) of embryos. In the absence of lab error (mislabeling or misidentification of the embryo) or abnormal gender mosaicisms, PGD for gender selection is highly accurate and a relatively simple PGD. One cell or at most two cells are removed from the embryo on day 3 of culture and  sent to a genetics testing lab to be probed with a fluorescent probe that will light up the sex chromosomes and allow identification of the cell (and thereby the remaining embryo) as one gender or the other. A lab report is produced and sent to the IVF lab so that the lab can identify each embryo as being male or female. Embryos  of the desired gender can then be transferred to the uterus. PGD for gender selection is most effective but also most expensive, because the costs of PGD (approximately $3000-$6,000)  is added on to the costs of IVF (approximately $12,000) and unlike sperm sorting, can’t be used with less expensive interventions like insemination.

PGD for gender selection or family balancing is condemned by some because embryos of the non-desired gender may be discarded by the patients who created them. It is important to understand that patients also have the option to donate their excess embryos for stem cell research or to other patients who would like to use them to have a child. Discarding embryos certainly is NOT mandatory and, in my opinion,  all choices regarding disposition should be left up to the intended parents who created the embryos.

Gender selection can also be used to prevent transmission of genetic diseases that are sex-linked to the next generation. Some genetic diseases like hemophilia are almost always observed in male children. A list of sex-linked diseases typically includes Hemophilia A, Duchenne muscular dystrophy, Lesch-Nyhan Syndrome and fragile X syndrome. Hemophilia A is a blood clotting disorder which can cause death from even the smallest cut. Duchenne muscular dystrophy is a muscle wasting disease. Lesch-Nyhan is a disease that causes cerebral palsy and self-mutilation. Fragile X syndrome causes mental retardation and other physical problems in females. Maternal inheritance of mitochondrial diseases is another category of genetic disease that is always passed on through on gender, the mother in this case. Some of these genetic defects in mitochondria cause a truly horrible decline in functioning and slow death for its unfortunate victims.

I realize that the topic of gender selection, particularly for non-medical reasons, has ignited some strong feelings among various groups. From my perspective, every child should be a wanted child and that organizing principle generally informs my opinion about reproductive choices in general. I realize that gender selection is often raised as an issue in the context of gender discrimination against women, but at least in my own clinical experience, I have not observed a preference of patients for boys. In my experience, parents who already have one or more children of the same gender, seek to have a child of the opposite gender and that is as often a girl as a boy. Once we had a couple who were interested in having both a boy and a girl but they wanted control over birth order, a boy first, then a girl. While this extreme need for control in family composition may trouble or offend some, it is not necessarily a bad thing. Parenting ability is independent of the use of gender selection. Parents often find out, whether or not they use gender selection, that their kids will develop pretty much independent of their own designs for them. We can influence, instruct and persuade our children, but in the end, they will be their own people.

 

 

© 2011, Carole. All rights reserved.

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