More and more couples and single women who want to have children are turning to assisted reproduction techniques. As a result, these techniques are constantly being improved and developed. But it is not just the methods themselves that are constantly evolving; new technologies are also emerging in the field of assisted reproduction. One such technology is MicroSort.

What is MicroSort(R)?

MicroSort is a technique for separating sperm based on the sex chromosomes they contain. It was developed in the USA in the 1980s. Initially, it was only used to separate sperm from bulls, so it originated in cattle breeding. In the 1990s, the technology was adapted to human sperm by the Genetics and IVF Institute in Virginia, USA.

Biological basis

The human chromosome set contains 23 pairs of chromosomes, a total of 46 individual chromosomes. The finished germ cells, however, contain only half the set of chromosomes, i.e. only one copy of each pair. The female germ cells are called eggs, and the male germ cells are called sperm. After fertilisation, the nuclei of the egg and the sperm fuse so that the embryo again has a complete set of chromosomes. Each pair of chromosomes is normally identical, except for the last pair, the sex chromosomes. In the mother, this pair consists of two X chromosomes. So when the set is split during the formation of the gametes, each egg still contains one X chromosome. This process is called meiosis. In the father, however, the last pair of chromosomes consists of an X and a Y chromosome. The sperm will therefore carry either one or the other. If the egg is fertilised by a sperm with an X chromosome, the biological sex of the embryo will be female; if it has a Y chromosome, it will be a boy. A man's sperm always contains approximately the same number of sperm of each sex.

The MicroSort(R) technology

The X chromosome is considerably larger than the Y chromosome. This characteristic is used in MicroSort to separate the sperm of the different sexes. First, the sperm are extracted from the semen and placed in a new medium containing proteins. A fluorescent substance is also added. This is followed by an incubation period to allow the sperm to absorb the substance. The whole mixture is then placed in a flow cytometer. This machine is responsible for separating the chromosomes. It uses an argon ion laser to illuminate each cell individually. The treatment with the fluorescent substance causes the sperm cells to light up. Because sperm with an X chromosome contain more genetic material, they light up faster and more intensely. This allows the machine to distinguish and separate the cells according to their sex. The sperm are then examined under a microscope by a laboratory technician and their motility is assessed. The cells remain in a nutrient medium to prevent them from "starving to death". A fluorescence microscope can also be used to assess whether the sperm have separated sufficiently. The X-linked sperm glow red, while the Y-linked sperm glow more green. Using this technique, the chances of having a girl in IVF with female sperm are about 93%, and the chances of having a boy in IVF with male sperm are about 73%.

Why use MicroSort(R)?

In livestock breeding, it is quite obvious why you would use such a technique. If you own dairy cows, for example, you would naturally prefer to have female offspring. With human babies, the situation is much more ethically questionable. From a medical point of view, however, there is an important reason. Many hereditary diseases are inherited in an X-linked way. A prominent example is Duchenne muscular dystrophy, in which muscle tissue cannot regenerate sufficiently and gradually turns into connective tissue. Patients often do not reach the age of 20. In such cases, the genetic defect is located on the X chromosome, usually the mother's. However, the mother herself does not have the disease. She has two X chromosomes, but the body's cells only use one of them at a time. The second X chromosome is rarely used in women and forms the so-called Barr's cells. If one of the two X chromosomes is defective, the body recognises this and uses the healthy X chromosome. It is only in the germ cells that both X chromosomes are present again. This means that the egg cell can also contain the defective X chromosome. If a female sperm is used for fertilisation, the disease will not break out because the girl can simply use the healthy X chromosome. The Y chromosome is much smaller and always needs extra information from the X chromosome. But because male offspring only have one X chromosome, the body has to use it, even if it is defective. This is why X-linked diseases almost always occur in male offspring. Sperm selection can prevent the onset of such diseases.

Disadvantages of the MicroSort(R) technology

The debate about designer babies is at least as old as IVF itself. As artificial insemination methods advance, there are more and more opportunities to choose the characteristics of the child, so to speak. This is ethically very questionable when you see in countries like China how female embryos are aborted because boys are more valued. To prevent gender discrimination, sperm separation methods are also banned almost everywhere.

However, surveys have shown that the majority of families want a boy to be the first born in the family. After that, however, the baby daughter is supposed to follow. The study was carried out by Dr Roberta Steinbacher of Cleveland State University in the USA*. She fears that a nation of small, hard stars will emerge**. The method would probably even be popular with the population.

In addition, such a procedure costs about 3,400 US dollars. But this price does not include the IVF itself. Of course, it can happen that several attempts are needed for a successful insemination. This also means that the separation may have to be carried out several times.

When and where is sperm separation allowed?

Due to various ethical and legal concerns, MicroSort technology is banned in all countries, as the FDA (Food and Drug Association) has not granted approval for this technology.

In all countries, sex selection is only allowed if there is a known family history of X-linked diseases. However, in MicroSort's home country, the USA, the technology is being promoted. There are two laboratories, one in Virginia and one in California, which are becoming increasingly popular. In the USA, it is allowed to choose the sex of the baby if there are hereditary diseases in the family and as part of family balancing. For example, if a family already has two boys and now wants a daughter, this technique can be used. Clinics in northern Cyprus also perform sex selection.

In principle, however, the desire to have children should never be made dependent on the sex of the child. In Central Europe, there is no social pressure on this issue and it should stay that way. Every child should be able to be a desired child, regardless of whether it is a boy or a girl.

Would you like to know more about equality in the family and the choice of gender?

There is only one place in Europe where sex selection can be performed. Treatment with IVF and genetic testing costs around EUR 6000 (excluding medication) and is carried out using PGT-A or NGS (Preimplantation Genetic Diagnosis), with a success rate of around 50% depending on age, which means you will need two cycles.