Oct 08 2007

Choosing the Sex of your Baby

A member of the SGU forum asked the following question:

I have a daughter that I love so much. But since I can not afford 20 more children and probably will only have one more, I would like to have a boy baby (Specialy my mom) hehe … many books on internet / and even doctors claim that they can help couples choose a certain gender. Is that a scam or can we really choose our next baby’s gender?

The short answer is that it is a scam (unless we are talking about artificial insemination, which I will discuss below).

First, some basic biology. Human DNA is divided into 23 different chromosomes, with each cell having a pair of each. One of those chromosome pairs are the sex chromosomes – which come in two flavors, X (female) and Y (male). Females have two X chromosomes, and males have one X and one Y. Eggs from the mother and sperm from the father each contribute one copy of the 23 chromosomes. Eggs can therefore only contribute an X, while 50% of sperm with be X and 50% Y. Therefore the sperm dictates the sex of the child.

Methods for influencing the sex of the child therefore focus on affecting which type of sperm, X or Y, fertilizes the egg. During insemination 10’s of millions of sperm are ejaculated with one ultimately fertilizing the egg. Various methods have been claimed to give an advantage to one type or the other. Some methods are based upon the fact that X chromosomes are slightly bigger than Y chromosomes, so it is believed Y sperm swim a bit faster. Methods include changes in diet, the timing of sex, and acidifying the vaginal canal. None of these methods are very plausible and none have been shown to be effective.

There are also countless “magical” methods that have been advocated over the centuries – methods without any putative biological mechanism but are little more than superstition.

The strong desire of many parents to choose the gender of their baby has spawned an industry of products and claims, but they amount to little more than snake oil and scams.

However, in the context of in vitro fertilization choosing the sex of the child is very possible. There are several methods that work well. You could fertilize several eggs, then do genetic testing to determine their sex prior to implantation. There are also methods for separating X sperm from Y sperm (mostly taking advantage of the different size of the chromosomes) and then fertilizing the egg with the sperm of the desired sex.

In vitro fertilization is expensive and time consuming, so only couples who cannot conceive naturally are likely to avail themselves of these methods. It is possible, though, for sperm separation techniques to eventually be available in a home kit, with insemination then taking place “turkey baster” style. Sure, a bit of the romance is lost, but if this becomes available you can bet it will be popular. But these kits are not available at present – the technology is not yet portable and automated enough.

I always like to speculate about how existing technology will advance in the future. The ability to choose the sex of a child by sperm sorting is just the beginning. What if you could go to a lab, or buy a home kit, that would enable you to select from the millions of sperm those that had the genes you desired (not just the chromosome)? At first such technology would likely be used to screen out for genetic diseases. Rather than playing genetic Russian roulette, simply remove the sperm that carry the mutation for that horrible genetic disease.

Once this technology is established (and who can argue against preventing horrible genetic diseases) it is a short trip to selecting for genes that are associated with a lower risk of common diseases. Why pass on that gene for high cholesterol you got from your father, when some of your sperm are carrying the gene from your mother that is associated with low cholesterol? Once the technology works it is likely to progress from preventing genetic diseases to reducing genetic risk for other disease, then to choosing genes that improve biological function (like vision and immune function), and then to height, eye and hair color.

This, of course, is not the same thing as genetic engineering – just genetic sorting. Why leave up to chance which genes you pass onto your children, when you can ensure that you pass on the best of your genes? The genes are still all yours, unaltered. You are not making a super-human, but giving your child the best you have to give. (Can’t you see the ad campaign now?)

Of course, once people are used to the idea of controlling what genes get passed onto their children, it is a short trip to the notion of inserting better genes into the mix. Why deprive your child of that gene that renders people immune to heart disease? It’s not your fault that you don’t have that gene, and why should your children suffer.

You see where this is going. I personally don’t have a problem with any of this, and also recognize that its largely does not matter what I think or anyone else alive today. These changes will come over time, with each generation getting used to the genetic manipulation that is available to them. Those people today who are squeamish about human genetic engineering will likely be considered old-fashioned and naive by later generations. There will also very likely be a subculture of genetic Luddites who refuse any genetic technology, and all power to them. I file this under personal choice and freedom, and argue that one of the fruits of technology is that it grants humans a greater range of choices.

This is why I understand the desire of parents to be able to choose the sex of their children. But this technology (outside of in vitro fertilization) is not yet here, so don’t buy the snake oil.

7 responses so far

7 thoughts on “Choosing the Sex of your Baby”

  1. Jim Shaver says:

    Reminds me of the movie GATTACA, which depicted a future world in which genetically engineered humans were known as “valids”, while naturally-born humans were called “in-valids”. The in-valids were treated as second-class citizens, held menial jobs, and essentially had no chance to aspire to anything better.

    While that vision of the future can be considered hyperbole in many respects, certainly the very real possibility of insurance companies, for example, discriminating against people with known genetic predispositions for certain diseases, etcetera, should not be taken lightly. Perhaps by the time that future arrives, we will have also figured out how to engineer a society that guarantees healthcare for all its citizens. But given the current US political climate, that doesn’t seem to be likely to happen anytime soon.

  2. daedalus2u says:

    Dr Novella, you didn’t mention the most commonly practiced methods of gender selection, sex determination in utero and selective abortion of the undesired gender (usually female), and the “old fashioned” traditional method of infanticide.

    In China gender selection is greatly skewing the ratio of males to females. In India there are those who advertise “better 500 rupees now than 50,000 rupees later”, meaning 500 rupees for ultrasound and abortion of a female fetus rather than 50,000 rupees for a dowry when she is to marry.


    In virtually all species the gender ratio is close to one. If it ever gets skewed, there is very strong selection pressure to bring it back (individuals who produce more of the rarer gender contribute disproportionately to the next generation).

    The skewing of the gender ratio in China and India will be corrected in future generations when the excess males are unable to find mates.

    My own opinion is that gender selection is inappropriate for any reason other than health considerations of the individual being conceived. If a person feels that they would not be able to love and/or provide appropriate care for a child of a particular gender, they should forgo being a parent.

  3. Robz says:


    I have 2 daughters so my wife and I have discussed sex selection and I investigated it a little bit at one point. Personally I would never do such a thing for family balancing but think of the potential philosophical, ethical and societal consequences of sex selection…

    What about the praticality of sperm sorting i.e. MicroSort. with intrauterine insemination (IUI) ?


    The site boasts the following
    “….Currently the sex selection for boys yields about a 73 pure sample, with 76 of the Ysort babies being boys and the sex selection for girls provides about an 88 pure sample, with 91 of the MicroSort® Xsort babies being girls. ……”

    Also MicroSort is doing clinical trials of new IUI techniques. It seems that this maybe a realistic non-IVF alternative. What do you think?

  4. ziggy says:

    “sex determination in utero and selective abortion of the undesired gender (usually female)”

    In the US, while not illegal this is generally considered unethical by most doctors and genetics laboratories. A little background: I am a cytogenetic technologist and have worked for 15 years doing clinical prenatal testing on amniotic fluid and chorionic villus specimens. At one time we had a client send us a steady stream of early gestation ( 10 -12 weeks gestation) amniotic fluid specimens. Normally, amniocentesis is performed around 15 weeks of gestation this is considered to be relatively safe for the fetus while early enough to give a diagnosis such as Down syndrome, etc. and providing time for the parents to terminate the pregnancy if they choose. Performing an amnioscentesis at 10 weeks can be very dangerous in that the fluid volume is much less and the area where the needle is inserted is much smaller resulting in a higher risk of actually injuring the fetus. There is really no sound medical reason to do this. However, if you want to determine the sex of the fetus and possibly terminate the pregnancy before people notice that you are pregnant this might be an option.
    Back to the point, our director had a few discussions with this client and it became very clear that he was running a sex selection clinic. We promptly refused all future test requisitions from that client.

    Microsort sounds promising and may very well lead to the ability to select other genetic traits from the father that Dr. Novella discussed in this post. If we can find a safe way to label the chromosomes of living sperm cells that have a specific gene we can then sort the sperm based on that label with similar technology. I believe there’s already a clinical trial do this with living blood cells to sort out cancerous cells.

  5. ziggy says:

    “Does exposure of a sperm cell to atmospheric air modify the phenotype of the individual conceived by that sperm cell?”

    This could easily be investigated by studying humans produced by in vitro fertilization and even artificial insemination. These procedures involve steps in which sperm are certainly exposed to atmospheric levels of oxygen as they are separated from the seminal fluid, transferred to and from multiple vessels, etc.

  6. daedalus2u says:

    In principle you are right, however if the difference due to exposure to air is small compared to natural variation it might be difficult to observe. For example, if it added 1/4 inch to an adult’s height.

    If the trait is more complex and difficult to measure, such as immune function, or muscle strength, or physical endurance it might be very difficult to observe differences.

    If the trait is extremely complex, such as personality, there is likely no way to observe differences unless they are quite extreme. There is no otherwise identical control group to compare. The precise phenotype developed by each genome occurs only once (except for monozygous multiple births) and so constitutes more of an “anecdote” than a representative sample of possible outcomes.

    If we do the thought experiment, where we take a million identical fertilized eggs with identical genomes and develop them into adults, there will be variation between all of them. None of them will be “identical”, even simple traits such as height will cluster around a mean, with some standard deviation. Development is fundamentally chaotic. The ultimate outcome of large systems of coupled non-linear parameters is not determinable from the starting conditions. Differential changes in starting conditions will produce macroscopic changes later on.

    The “details” of brain structure are obviously important in some ways, but that is something we have very little knowledge of, and insight into, and it is not something that we can do experiments on in humans, and certainly not with even modest n number.

    In the example of exposure of sperm to air, it would be easy to show experimentally that certain changes are less than a certain amount. There have been enough people conceived this way that any potential adverse effects are fairly small. Showing that those changes are actually zero is not something that could ever be achieved experimentally. If development was sufficiently understood, and it was known that there were no developmental pathways that were affected by exposure to air at those stages of development, the hypothesis of no effect might be pretty credible. I think we are a very long way from understanding development well enough to know that. Signaling by hypoxia and oxygen is well known to be important in the first trimester. Is it important before then?

    In the context of the discussion of effects of sperm sorting, any vender who (at this time) claims to know that there will be zero adverse effects is pushing snake-oil.

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