What is the implantation of the fertilized ovum?

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Embryo implantation is the process by which the embryo is anchored in the endometrium and is essential for pregnancy to occur. From that moment the placenta will begin to form to allow the nutrition, sustenance and protection of the future baby during pregnancy.

Below you have an index with all the points that we will discuss in this article.

Index

What is the implantation of the fertilized egg? - Stages step by step

Knowing why some embryos implant and others is not one of the challenges of reproductive medicine. The intimate knowledge of the physiological aspects of this process is important to design strategies that increase the chances of pregnancy.

Only one third of cycles considered fertile end in pregnancy. The cause of this low success rate is due to several factors such as an inappropriate uterine environment (since there must be a hormonal environment conducive to estradiol and progesterone), a poor embryo quality , a low receptivity of the maternal endometrium and a defective dialogue between both (embryo-endometrium).

The rate of clinical pregnancy per menstrual cycle in couples considered fertile who maintain regular relationships without contraceptives is 25-30%.

This rate is relatively low compared to other animal species, although it is cumulative, that is, it increases month by month, reaching 80% after 10 months. However, it decreases with the increase in the age of the woman.

Years ago, the treatment of implantation was limited to the use of luteal phase support protocols by the administration of progesterone and hCG ( human chorionic gonadotropin ).

Currently, several basic and clinical studies on this subject have allowed to know the role played in the implantation of different cell populations of the uterus and the role of some molecules such as cytokines or integrins, adhesion molecules and growth factors.

What is needed for there to be an implantation?

There is evidence that cytokines and growth factors play an important role as local mediators of the actions of steroid hormones on the endometrium, in order to prepare it for implantation.

It is believed that signals from the preimplantation embryo could induce the production of cytokines by the endometrium. These, in turn and by binding to specific membrane receptors, would activate the expression of adhesion molecules such as integrins, responsible for mediating the adhesion of the blastocyst to the endometrium.

Biologically, it is a complex process where a blastocyst embryo is fixed to the receptive endometrium of the mother. There must be a total synchronicity between embryo and endometrium. Therefore, for implantation to occur it would be necessary to:

  • The fertilization of the ovum by the spermatozoon
  • The proper development of the embryo up to blastocyst
  • The journey from the embryo to the uterus
  • The receptivity of the endometrium
  • The interaction of the molecules produced by the embryo and the endometrium


When does the implantation occur?

The implantation takes place in the middle third of the posterior face of the uterus and happens during a specific period of time, in which the dialogue between the embryo and the endometrium of the mother is possible.

This moment is called the implantation window and comprises from the 20th day of the cycle until the 24th (around day 6-7 after fertilization) in a standard 28-day menstrual cycle.

The implantation window is the period in which the endometrium is receptive to the embryo and therefore allows adhesion of the blastocyst.

The change from non-receptive to receptive endometrium only occurs if the appropriate hormonal environment exists and if the blastocyst expresses the appropriate molecules to induce it (selectins, cytokines, etc.).



Interview with Dr. Silvia Jiménez (Reprofiv)

In the following video, Dr. Silvia Jiménez, director of the laboratory of the Reprofiv clinic, explains all the details about the process of embryo implantation and when it occurs.

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