Much has been discovered in recent decades about eggs, sperm and embryos. Thousands and thousands of studies have detailed these essential actors for the reproductive process, clarifying previously obscure issues. Although we are far from fully understanding the dynamics involved, we have already made great strides.
However, little is known about the endometrium. It is still a mysterious element, little studied and little talked about. There are those who do not believe in its relevance, delegating to it a secondary or even tertiary role, as a passive agent in the reproductive process.
We don’t understand it that way. We believe that the endometrium is an active agent in the embryonic implantation process. The endometrium can even select the embryo to implant, preventing embryos with malformations from settling in the womb and leading to the birth of a child with syndromes.
Obviously, this process is subject to imperfections and failures, and it is precisely in these imperfections that the endometrial study can bring us countless answers and contribute to significant improvements in the embryo implantation rates.
Below, we describe which elements can be analyzed and which are supported by the medical scientific literature.
ENDOMETRIAL ASPECT TO ULTRASOUND
It is the oldest and simplest criterion to be analyzed. Corresponds to the visualization of the thickness and aspect of the endometrium on ultrasound examination.
As for appearance, the endometrium can be of three types:
Linear: when we are in the menstrual period and it does not usually exceed 5.0 mm;
Triple or tri-laminar: we have this pattern when there is an effect of female hormones on the endometrium. It is the desired pattern during ovarian stimulation or during preparation to transfer embryos;
Hyperechoic or hyperechogenic: the endometrium is completely white, showing that there is an adequate progesterone effect. We observed this pattern after embryo transfer or after ovulation.
As for the thickness, the medical literature reports pregnancy from 5 mm. Values lower than this are a poor prognosis for obtaining pregnancy. The best results are obtained when we have an endometrium measuring at least 7 mm in thickness on ultrasound. There is no maximum endometrial thickness value for pregnancy to be successful, although some studies place the maximum thickness of 14 mm or 18 mm as a cutoff point.
It is the specific period in which the embryonic implantation can happen. In this period the endometrium undergoes changes both in its morphological structure and in the production of substances. These changes must occur synchronously with the fertilization of the eggs and the arrival of the embryo in the uterus. The implantation window is believed to last only five days, between the 20th and the 24th in a 28-day menstrual cycle.
Who defines the beginning of the implantation window is ovulation and progesterone production. Then the window starts on the sixth day after ovulation and ends on the tenth day after it.
If the embryo reaches the uterus before or after the implantation window is established, it does not implant and pregnancy does not happen.
Other consequences may be due to defects in the implantation window. It can be out of place and happen before or after the predicted time (for example before the 20th of the cycle or after the 24th of the cycle). When this occurs, the embryo reaches the endometrial uterine cavity and does not find the implantation window “open” and pregnancy does not happen.
The implantation window can also be very short (less than 5 days) and in this situation – we believe – we observe implantation failures, which are those cases in which the patient receives embryos of excellent quality and, even so, they (nor so inexplicably …) do not implement.
The opposite, when we have a very long implantation window, the endometrium does not correctly select the embryos and allows any altered embryo to implant itself. Obviously, these altered embryos are largely unable to maintain their development and we have an abortion. This situation, a very wide implantation window, can explain the cases of recurrent abortions.
Plasmocytes: are cells derived from type B lymphocytes, involved in the production of antibodies. We observed an increase in the presence of these cells when we have an infection in the endometrium, endometritis, which can be extremely harmful for implantation and pregnancy. Endometritis, when it is chronic, does not give symptoms (neither fever, pain, discharge, smell or bleeding) and goes unnoticed, preventing the success of treatments.
NK cells (Natural Killer) – CD16 / CD 56 Plus: are defense cells of the organism, acting against foreign organisms and cancer cells. It is believed that NK cells can have their function altered and thus start to attack embryos, understanding that they are foreign to the organism, not allowing its implantation.
There is strong evidence in the medical literature that when the patient’s endometrium has an imbalance in the expression of NK cells, with an increase in the CD16 + / CD56 + ratio, there is a reduction in embryonic implantation. There are also numerous scientific studies showing that the administration of a substance called Human Immunoglobulin after embryo transfer or in the first trimester of pregnancy can reverse this situation, facilitating implantation and reducing the risk of abortions.
Endometriosis nerve fibers (PGP 9.5): these are nerves found in the endometrium of patients with endometriosis. They are an important marker for the disease, preventing the patient from having to undergo surgery (videolaparoscopy) to be diagnosed with endometriosis.
Nerve fibers (black arrows) present in the endometrium of a woman with peritoneal endometriosis (immunohistochemical determination of PGP 9.5).
ERA test (Endometrial Receptivity Array): The ERA test is a genetic test of the endometrium, marketed by the company Igenomix, linked to the group of doctors and researchers from the IVI (Instituto Valenciano de Infertilidade) of Spain.
The ERA provides a profile of gene expression in the endometrium with a sample obtained by biopsy during the implantation window period. This gene profile can demonstrate whether the endometrium is receptive or not receptive to the embryo, as some genes are more active and others less (this normally occurs in the body) during the implantation period. If there is a change in this expected profile, the deployment may not occur.
The ERA test is extremely rich in scientific information that may one day bring many responses to embryonic implantation disorders.
However, at present, the ERA test is of little clinical applicability. When faced with a pattern of genes that configure an “unreceptive” endometrium, for example, there is nothing or very little to do for this patient. Firstly, because there is not enough medical technology to alter genes that are defective and, even if there were, genetic manipulation is a crime in Brazil and in practically the whole world. We therefore have a scientific and a legal barrier to be able to proceed with studies about ERA.
Example of a gene profile obtained by the ERA test. On the left we have a pattern of genes from the proliferative phase of the endometrium (before ovulation). On the right we see 3 patterns: pre-receptive, receptive and post-receptive. Only in the “receptive” pattern can pregnancy occur normally.
Endometrial biopsy: The terms “scratching” or “endometrial injury” are also used interchangeably. Endometrial biopsy is a minimally invasive procedure, performed in the doctor’s office, without the need for anesthesia or a surgical center. Due to its simplicity, the cost is also much lower than that of a hysteroscopy, for example, in addition to presenting much lower risks.
During endometrial biopsy, a thin plastic catheter, called Pipelle de Cornier, is introduced through the cervical canal and reaches the endometrial cavity. Through a suction mechanism, as in a syringe to collect blood, the endometrium sample is obtained.
For the patient, the discomfort is minimal, with mild pain or no pain and no bleeding.
The sample obtained can then be sent to the numerous existing tests on the endometrium. We prefer our clinic to perform immunohistochemical analyzes on endometrial samples. We have a range of important information obtained and which provide answers to implantation failures, as well as can define treatments, such as the use of antibiotics, more or less preparation time with Progesterone to correct changes in the implantation window, use of human immunoglobulin, of anticoagulants, among other interventions.
It is for this reason that the immunohistochemical analysis is much richer than the ERA test, since the information obtained here is very poor and brings little intervention capacity based on the result.
Endometrial sample obtained with the “Pipelle” catheter. On the left, the drawing shows the vacuum created when we pull the plunger from the catheter. In the center, we have the moment when the catheter reaches the endometrium and on the right, the small portion of the endometrium obtained by suction, which will be used for the analyzes.
There is also a very interesting adverse effect obtained when performing an endometrial biopsy: the increase in embryonic implantation rates.
The exact reason for this event is not yet known, probably the biopsy changes the pattern of endometrial immune response, providing greater chances of implantation in subsequent cycles. There is also the possibility of causing a scar in the endometrium, a place that begins to produce adhesive substances that would favor embryonic implantation.
This effect was first noticed by an Israeli researcher, Barash, in 2003, who observed twice the chances of implantation in patients who had undergone endometrial biopsy in a cycle prior to the IVF treatment.
These results were confirmed by us in 2011, when the preliminary results of Dr. Fernando Prado’s PhD thesis on endometrial proteins and embryonic implantation were analyzed. These data were presented on the 27th. European Congress on Human Reproduction and Embryology in Stockholm – Sweden, with great prominence from the national and international media at the time.
Referências na Literatura Médica:
- Diagnosis of endometriosis by detection of nerve fibres in an endometrial biopsy: a double blind study. Al-Jefout et al. Human Reproduction, 24(12): 3019-24, 2009.
- Natural Selection of Human Embryos: Impaired Decidualization of Endometrium Disables Embryo-Maternal Interactions and Causes Recurrent Pregnancy Loss. Salker M, Teklenburg G, Molokhia M, Lavery S, Trew G, et al. PLoS ONE 5(4): e10287. (2010). doi:10.1371/journal.pone.0010287.
- Local injury to the endometrium doubles the incidence of successful pregnancies in patients undergoing in vitro fertilization. Barash A, Dekel N, Fieldust S, Segal I, Schechtman E, Granot I. Fertility and Sterility 2003; 79:1317–22.
- Local endometrium injury/healing increases embryo implantation and pregnancy rates of in vitro fertilization treatments. Bueno, M. B. ; Ferreira, F. P. ; MAIA FILHO, V. O. A. ; Rocha, AM ; SERAFINI, P ; MOTTA, Eduardo Leme Alves da . Human Reproduction (Oxford. Print), v. 26, p. i205-i206, 2011.