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There are many parents who, for a variety of reasons, have a desire to choose the sex of the baby they would be trying for.

This is a very controversial area but it is neither the intention nor the purpose of this article to go into the merits or otherwise of pursuing the goal of choosing the sex of one’s baby. We are looking at the methods available and whether they work or not.

The general probability:

Any prospective parent or parents would (or should) be aware that their chance of getting a baby of the desired gender is roughly 50%. It sounds obvious but it is a fact that is not always looked at objectively by some.

High-tech methods for sex determination:

We start by looking at these because they are the clearest with a proven scientific basis and track-record.

Through in-vitro fertilization (IVF), it is possible for parents to choose and be virtually guaranteed of the gender of their baby. First of all, let’s look at how a baby ends up being a boy or a girl:

A woman’s egg does not have any role in determining the sex of the baby. This is because the egg will always carry the X chromosome. A man’s sperm, on the other hand, will either have an X or a Y chromosome (never both).

When the woman’s egg is fertilized by a sperm carrying an X chromosome, the resulting embryo will have XX sex chromosomes and will therefore be a girl. If the egg is fertilized with a sperm carrying a Y chromosome, the embryo will be XY and therefore a boy. That is the foundation of natural gender assignment.

In natural conception, a man’s ejaculate will have millions of spermatozoa, with roughly half of these carrying an X chromosome and the other half carrying a Y chromosome. All these, and there could be as many as 20 million of them, will scramble to reach the egg first. Once one has penetrated the egg capsule, the door is shut for the rest. The ‘winning’ sperm will determine whether the resulting embryo will be a boy or girl.

Sex determination in IVF

We have seen what happens naturally. With assisted conception methods, it is possible to get as close to 100% as is humanly possible in determining the sex of the baby.

Determining sex via Intrauterine Insemination (IUI)

In assisted conception, IUI is the least high-tech method of achieving a pregnancy and also the least expensive. IUI involves taking semen from a male partner, preparing the sperm from this and injecting this using a syringe into the woman’s vagina or womb. The injecting is made to coincide with ovulation to maximize the possibility of successful conception.

The IUI method can be used to try to get a baby of a specific gender. This is how it is done:

A special fluorescent dye is applied to the sperm to allow to distinguish X carrying from Y carrying sperms. In simple terms, when a laser beam is applied to the sperm, the larger X carrying spermatozoa will be found to have absorbed more dye and therefore glow brighter. These are then separated from the smaller Y carrying spermatozoa. Now, depending on the sex desired by the prospective parents, the appropriate group of spermatozoa is injected into the womb. If a boy is desired, the ‘Y’ will be injected and if it is a girl wanted, the ‘X’ will be injected.

Success rate of IUI in determining baby’s sex

In relative terms, IUI is easy to perform. That is the method’s strength. However, its major weakness is its modest success rate. To begin with, the possibility of a successful conception is about 1 in 6 (about 16%). This is significantly lower than IVF (see below).

Moreover, even if conception happens, there is no guarantee that you will end up with a baby of the desired gender. This is because, the process of separating the two groups of spermatozoa described above is not foolproof. The success is variably quoted at between 75 – 90%, which is clearly better that the coin-toss of natural conception but also, crucially, not 100%. Interestingly, the success rate is higher for those looking for a girl where it is consistently close to 90%.

IVF in baby sex determination

The technology now exists in determining the sex of the baby. The impetus for the technology was mainly the very distressing inherited genetic conditions which affect children of one gender or another. Take an example of Duchenne muscular dystrophy. This is an X-linked recessive disorder. This means the responsible defective gene is carried within the X chromosome. Girls can carry the defective gene but because they have a second X chromosome with a normal gene, they are not affected by this condition. Boys, on the other hand have only one X chromosome. This means, if that chromosome (inherited from the mother) carries the defective gene, the child will be affected. The condition is quite severe characterised by progressive muscle weakness, paralysis and eventually death. Affected boys are usually already wheel-chair bound by the age of 12 (sometimes a lot earlier) and death ensues in the 20s or 30s.

Parents with a child so affected may wish to avoid having another child with this debilitating condition and severely curtailed life expectancy. There are two ways of doing this, both via the IVF technology. One would be to have the male embryos produced tested for the defective gene and transferring those not affected. The other is to transfer only female embryos as these have no possibility of being affected by this condition. This is where pre-implantation gender determination (PGD) comes in. There is little or no controversy about this sort of application of the technology.

Pre-implantation gender determination is 100% reliable. In other words, there is no practical possibility of getting it wrong via this method. What is more, for most women, the chances of a successful conception via IVF are significantly higher when compared to IUI (above). However, it remains quite expensive and is unavailable in many parts of the world.

Continues next page

In vitro fertilization (IVF) allows for pre-implantation gender determination that is 100% reliable. The ethics of the practise is a whole different matter

In natural conception, millions of spermatozoa race to get to the egg first as only one will be able to fertilize it thereby determining the sex of the resulting baby

Choosing a baby’s sex