The egg and the sperm are introduced to each other: the fertilisation process

After several hours in culture, the eggs are brought into contact with the sperm in order to achieve fertilisation.

What does conventional In Vitro Fertilisation entail?

IVF is one of the most frequently used techniques in assisted reproduction. It consists of bringing the egg and the sperm together to ensure that both genomes combine. When the semen sample is normal and there is a history of earlier fertilisation, “conventional” insemination is performed. This consists in placing the eggs in contact with a specific concentration of processed sperm (one hundred thousand sperm with good motility) in culture medium and incubating them at 37ºC until fertilisation is observed.

How is introcytoplasmic sperm injection performed? When is it necessary?

When the sperm sample is of low quality or there is no prior history of fertilisation, the insemination technique used is IntraCytoplasmic Sperm Injection (ICSI).ICSI is a highly sophisticated technique, requiring a great degree of precision, expertise and experience by the embryologist. It is the introduction by injection of a “live” sperm into the cytoplasm of the egg.
In the case of the Egg Donor Programme, ICSI is absolutely necessary, regardless of the quality of the semen, in order to ensure a high rate of fertilisation.

Seventeen to twenty hours after insemination, the eggs are observed under an inverted microscope at 400x magnification to see whether or not fertilisation has occurred. A fertilized egg has two pronuclei: the female pronucleus and the male pronucleus. We can see eggs which have been correctly fertilized, eggs that did not fetilized and eggs which have fertilized in an anomalous way.

Do all eggs fertilize after in vitro fertilisation?

No. Under normal conditions, using sperm from the ejaculate, the rate of fertilisation both in IVF and IVF-ICSI is about 70%.
The first cycle of IVF can be considered as diagnostic and allows the medical staff to determine the couple’s level of fertility. In some cases, we can find low levels of fertilisation (5-20%) or even complete fertilisation failure.

Are chromosomal embryo abnormalities more frequent in IVF than in natural conception cycles?

No. Although the average age of patients that undergo their first IVF treatment is higher than in the general population, and, therefore, the risk of embryo abnormalities higher, the rate of genetic abnormalities in children born after IVF treatment is similar to that found in natural conception.