It's time to pay attention to the endometrium

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Normally in reproduction the endometrium receives less attention than the ovary. However, this is changing in recent years and there are currently many studies that study the importance of knowing the morphology of the endometrium and determine if there is a defect in the luteal phase that can cause failures in the implantation.

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

Index

It's time to pay attention to the endometrium

One of these investigations has led to the appearance and clinical use of a new method that allows us to know the best time for implantation. It is the ERA method that we explain below.

Despite this new technology, ultrasound control continues to be key to determining the endometrial pattern, thickness and contractility, with the aim of predicting and avoiding implantation failures .

Array of endometrial receptivity

Currently, with the appearance of microarrays, the endometrium and the menstrual phases of the cycle have been approached from a genomic and proteomic pattern. Thanks to these microarrays, genes that regulate the window of implantation have been determined. These biomarker findings help clinically identify the moment of implantation.

The array of endometrial receptivity, ERA for its acronym in English (Endometrial Receptivity Array), is a novel technique that assesses whether the endometrium is in adequate conditions for embryo implantation. Therefore, a personalization tool for the transfer of embryos is offered, increasing the chances of success of fertility treatment.

In almost all these studies on gene expression, endometrial biopsy is used, which is performed at two different moments of the cycle to compare receptivity:

  • A sample after two days after ovulation
  • Another sample after seven days

This study in two different times, in the same patient and during the same cycle poses a problem, since it is believed that the first sample taken can cause inflammation and impair the expression of endometrial genes in the second biopsy.

Pay attention to the endometrium

Ultrasound control of the endometrium

As a non-invasive technique, vaginal ultrasound allows us to study the endometrium during the entire menstrual cycle. In assisted reproduction, during ovarian stimulation, the thickness and endometrial pattern are measured in a standard way to assess the receptivity of the endometrium and specify the best day of the embryo transfer.

Currently, uterine contractions during embryo transfer and the impact they can have on pregnancy rates are also being measured ultrasonographically. Both in IVF cycles and in natural cycles, uterine contractions decrease from the peak of LH, being minimal in the middle of the luteal phase. The administration of progesterone in IVF cycles decreases the frequency of these contractions and improves implantation.

It is believed that the good pregnancy rate achieved with blastocyst transfers on day 5 could also be related to the reduction of uterine contractions by the administration of two more days of progesterone, compared to the transfers made on day 3.

In oocyte donation programs or in frozen embryo transfers, vaginal ultrasound plays a fundamental role in confirming that the endometrium is ready. The only hormones needed to prepare the endometrium are estrogen (E) and progesterone (P).

Endometrial thickness

The objective to carry out the embryo transfer is to achieve an endometrium with an adequate thickness. It seems that an ideal endometrium is one that reaches more than 7 mm. with a trilaminar pattern. Endometrium less than 6 mm. They are associated with low term pregnancy rate.

In certain patients, a good endometrial thickness can not be achieved. In some cases, this is related to Asherman's syndrome or the use of clomiphene citrate in ovarian stimulation. It has also been observed that thin endometriums that do not respond to the action of estrogen could be related to the prolonged use of contraceptive pills for more than 10 years.

Why is there a low implantation rate in thin endometriums?

Currently, two main reasons that answer this question are posited:

  • Because of the existence of an anomaly in the estrogen receptors.
  • The oxygen tension in the endometrium.

The oxygen tension decreases during ovulation and at the moment of implantation but in endometriums smaller than 7mm, where the functional layer does not exist or is thin, the implantation of the embryo would be made in the basal layer that is more vascularized and where the tension of oxygen is much higher. It is known that high oxygen tensions are detrimental to embryonic development, which could explain that in these cases there were implantation failures.

The finding of cytokines that induce endometrial growth, together with the future discovery of new biomarkers that determine the implantation window and new ultrasound techniques to follow endometrial development or contractility, predict a promising future to improve implantation rates.

Source: Fertility and Sterility_ Vol. 96, No. 3, September 2011


colposcopies in Alicante(Spain)

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