How Do They Choose the Best Sperm for ICSI?

By BSc, MSc (embryologist) and BA, MA (fertility counselor).
Last Update: 01/12/2015

Many couples have difficulties to form a family. If after a year trying to achieve pregnancy, it has not been obtained, the couple must turn to a fertility clinic. Assisted reproductive techniques allow many couples to achieve the so long desired pregnancy.

Once the couple visits the specialist, after analysing their case, the doctor will recommend the best treatment, with which the couple will have the best likelihood of succeeding. The key to this success resides in the fact that the woman goes through ovarian stimulation, while the man is performed a spermatozoa selection.

Spermatozoa capacitation

Selection of the spermatozoa

The main assisted reproduction techniques are artificial insemination, conventional IVF and ICSI. In all these techniques, a selection of the spermatozoa is performed, named spermatozoa capacitation.

This selection also happens naturally. Once the ejaculation has taken place, the spermatozoa have a long way until reaching the Fallopian tubes, where the egg is waiting to be fertilised. During this way, only the best spermatozoa will reach their goal. Along their path, the capacitation or activation takes place, which allows the spermatozoa to recognize the membrane of the egg and penetrate in it.

In a fertility treatment, the expert performs a sperm capacitation, selecting the best spermatozoa so that they can be used in the recommended technique. As part of the routine, this selection is carried out through the spermatozoa motility. There are mainly two techniques: density gradient and swim up. Both of them consist on separating the progressive motile spermatozoa from the ones that aren’t. This way, only the best spermatozoa are used for insemination or in vitro fertilisation.

Improving the spermatic selection

With the advances in assisted reproduction, new techniques have been developed. One of them is related with the selection of the spermatozoa that present a high rate of spermatic DNA fragmentation. This method is named annexin V columns or MACS that stands for magnetic-activated cell sorting.

It is a technique that is used with repetitive failures in IVF, or patients with male infertility due to DNA fragmentation of the spermatozoa. The spermatozoa that show a damaged DNA will have apoptosis markers. It’s a cellular control system: when a cell presents severe damage, it’s destined to a programmed cellular death. With the annexin V columns, the spermatozoa that show fragmentation are magnetically separated from those that don’t have any.

When a spermatozoon presents damage in the DNA, it has a protein named phosphatydilserine. In the laboratory, a solution with annexin V linked to some metallic spheres, named microbeads, is added to the sample. When the sample is put through the magnetic columns, the damaged spermatozoa adhere to them.

It is a more precise selection of the spermatozoa, since it isn’t solely based on progressive motility, but also on the DNA of the spermatozoa.

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Authors and contributors

 Cristina Mestre Ferrer
Cristina Mestre Ferrer
BSc, MSc
Embryologist
Bachelor's Degree in Biological Sciences, Genetics & Human Reproduction from the University of Valencia (UV). Master's Degree in Biotechnology of Human Assisted Reproduction from the UV and the Valencian Infertility Institute (IVI). Embryologist at IVI Barcelona. More information about Cristina Mestre Ferrer
Adapted into english by:
 Sandra Fernández
Sandra Fernández
BA, MA
Fertility Counselor
Bachelor of Arts in Translation and Interpreting (English, Spanish, Catalan, German) from the University of Valencia (UV) and Heriot-Watt University, Riccarton Campus (Edinburgh, UK). Postgraduate Course in Legal Translation from the University of Valencia. Specialist in Medical Translation, with several years of experience in the field of Assisted Reproduction. More information about Sandra Fernández

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