The endometrium is the inner lining of the uterus. It is a layer that varies throughout the menstrual cycle, with the purpose of allowing the embryo to implant in it in order to give rise to gestation.
Taking this premise into account, in assisted reproduction treatments (ART) it is of vital importance to control that the endometrium has the appropriate characteristics to favor embryo implantation.
For this reason, there are several tests that can be performed to assess the patient's endometrium prior to embryo transfer. The aim is to ensure that the endometrium is in the best condition to receive the embryo.
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How does the endometrium change?
The endometrium is composed of a basal layer and a functional layer. The basal layer is responsible for producing a new functional layer each cycle, as this functional layer is regenerated each month in the event that no gestation has occurred.
To this end, the endometrium undergoes changes throughout the menstrual cycle. These variations are driven by estrogens and progestogens produced by the ovary. In this way, the endometrium goes through different phases:
- Proliferative phase: the stromal cells and endometrial glands increase due to estrogenic influence. This phase takes place until ovulation, i.e., day 14 of the menstrual cycle.
- Secretory phase: glandular secretion of substances necessary for embryo implantation. This change occurs in response to progesterone released by the ovarian corpus luteum after ovulation.
If pregnancy has not occurred, the degeneration of the corpus luteum leads to the shedding of the endometrium, which will be expelled with menstruation.
You can learn more about endometrial changes in this link: What is the endometrium - Thickening, types and pathologies
Tests for endometrial assessment
The embryo should implant in the endometrium approximately 6 days after fertilization. For this, not only is the quality of the embryo important, but the condition of the endometrium plays an equally decisive role. In addition, embryo and endometrium must be synchronized.
Currently, there are several tests that can be performed to assess the status of the endometrium.
Ultrasound monitoring of the endometrium
As a non-invasive technique, vaginal ultrasound allows us to study the endometrium throughout the menstrual cycle. In assisted reproduction, endometrial thickness and pattern are evaluated in a standard way to assess and estimate its receptivity.
Ideally, in order to perform the embryo transfer, the endometrium should be of adequate thickness. It seems that an ideal endometrium is one that reaches 7-9 mm in thickness and with a trilaminar pattern. A thin endometrium appears to be associated with lower pregnancy rates.
In egg donation programs or frozen embryo transfers, vaginal ultrasound plays a fundamental role in confirming that the endometrium is ready to receive the embryo. In these cases, the endometrium must be prepared in advance by administering hormones (estrogens and progesterone), or by taking advantage of the natural cycle if the woman still has regular menses.
Assisted procreation, as any other medical treatment, requires that you rely on the professionalism of the doctors and staff of the clinic you choose. Obviously, each clinic is different. Get now your Fertility Report, which will select several clinics for you out of the pool of clinics that meet our strict quality criteria. Moreover, it will offer you a comparison between the fees and conditions each clinic offers in order for you to make a well informed choice.
Endometrial receptivity test
In assisted reproduction cycles, a great effort is made to obtain optimal embryo development. Subsequently, a selection is made among the available embryos in order to transfer the one that will have the best chances of success. However, this would be of no use if the embryo is transferred into an endometrium that is not exactly at the right time to receive it.
This phase is known as the window of implantation and, in women with regular cycles, usually corresponds to days 19-21 of the menstrual cycle. However, this window of implantation may be displaced in time in some women, which may result in failure to achieve pregnancy after several attempts with good quality blastocyst transfer.
Nevertheless, there are tests available for the analysis of endometrial receptivity. These tests are performed on the basis of an endometrial biopsy and indicate whether the endometrium is receptive or not. If the endometrium is receptive, the embryo transfer will be performed under the same conditions as the biopsy. In the event that the endometrium is not receptive, the results would indicate when the embryo transfer should be performed.
Endometrial receptivity tests allow for a more personalized embryo transfer, increasing ART success rates.
If you are interested in this type of endometrial receptivity test, we recommend you read this article: What is the ERA endometrial receptivity test, and what is it for?
Study of the endometrial microbiome
This type of test analyzes the endometrial flora or microbiome, that is, the microorganisms found in the endometrium. Thus, based on an endometrial biopsy, the test provides a result as to whether the endometrial microbiome is suitable for embryo implantation to occur. This is because an imbalance in the endometrial flora could hinder embryo implantation.
If the endometrial flora is not dominated by Lactobacillus, it will not be the most favorable to host the embryo. In this case, the test report will recommend a personalized treatment with probiotics or antibiotics, depending on the result.
However, there is also a test that detects the main bacteria causing chronic endometritis (inflammation of the endometrium). This test is also very important to improve the results of ART, especially when there is recurrent implantation failure since chronic endometritis is present in a high percentage of these patients.
FAQs from users
Is endometriosis the same as endometritis?
Endometrititis and endometriosis are different concepts.
Endometritis is the inflammation of the endometrium caused by different reasons such as an operation or uterine manipulation after childbirth, abortion, IUD insertion, etc.
Endometriosis, on the other hand, is a proliferative disease of a benign nature, but highly damaging to the reproductive system.
Read more
Can endometrial thickness be improved wit natural remedies?
Endometrial thickness grows naturally in the middle of the cycle in women who have regular cycles . Drugs and supplements with anti-inflammatory effects should be avoided to avoid interfering with normal endometrial growth.
Abundant hydration and daily physical exercise, along with a varied diet and a healthy lifestyle, will promote the natural growth of the endometrium. In patients without periods (menopause) or patients with very irregular menstrual cycles, it will be necessary to administer drugs to help the endometrium grow.
How much does the ERA test cost?
The cost of this diagnostic technique varies from clinic to clinic. The approximate costs are $800 in which costs for fertility medication and endometrial biopsy are not included.
What endometrial thickness is needed to perform IVF?
Ideally, in order to perform an embryo transfer after an IVF cycle, the endometrium should reach a thickness of about 8 mm and present a trilaminar aspect by ultrasound.
However, an endometrial thickness of 8 mm does not guarantee that the embryo will implant. Similarly, gestation is also possible with thinner endometria, although these endometria result in lower pregnancy rates.
Recommended readings
If you would like to learn more about how the endometrium is prepared in assisted reproductive techniques (ART), you can read the following article: Endometrial preparation for embryo transfer.
If, on the other hand, you are interested in learning more about the embryo transfer process, we recommend you to visit this link: Embryo transfer: when and how is it done?
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References
Bu Z, Sun Y. The Impact of Endometrial Thickness on the Day of Human Chorionic Gonadotrophin (hCG) Administration on Ongoing Pregnancy Rate in Patients with Different Ovarian Response. PLoS One. 2015 Dec 30;10(12):e0145703.
Enciso M, Carrascosa JP, Sarasa J, Martínez-Ortiz PA, Munné S, Horcajadas JA, Aizpurua J. Development of a new comprehensive and reliable endometrial receptivity map (ER Map/ER Grade) based on RT-qPCR gene expression analysis. Hum Reprod. 2018 Feb 1;33(2):220-228.
Moreno I, Codoñer FM, Vilella F, Valbuena D, Martinez-Blanch JF, Jimenez-Almazán J, Alonso R, Alamá P, Remohí J, Pellicer A, Ramon D, Simon C. Evidence that the endometrial microbiota has an effect on implantation success or failure. Am J Obstet Gynecol. 2016 Dec;215(6):684-703.
Moreno I, Simon C. Relevance of assessing the uterine microbiota in infertility. Fertil Steril. 2018 Aug;110(3):337-343.
Simón C, Gómez C, Cabanillas S, Vladimirov I, Castillón G, Giles J, Boynukalin K, Findikli N, Bahçeci M, Ortega I, Vidal C, Funabiki M, Izquierdo A, López L, Portela S, Frantz N, Kulmann M, Taguchi S, Labarta E, Colucci F, Mackens S, Santamaría X, Muñoz E, Barrera S, García-Velasco JA, Fernández M, Ferrando M, Ruiz M, Mol BW, Valbuena D; ERA-RCT Study Consortium Group. A 5-year multicentre randomized controlled trial comparing personalized, frozen and fresh blastocyst transfer in IVF. Reprod Biomed Online. 2020 Sep;41(3):402-415.
FAQs from users: 'Is endometriosis the same as endometritis?', 'Can endometrial thickness be improved wit natural remedies?', 'How much does the ERA test cost?' and 'What endometrial thickness is needed to perform IVF?'.
Authors and contributors
More information about Cristina Algarra Goosman
Hi, I’ve had two IVF cycles and I can’t get pregnant, the babies don’t come out, a friend told me that maybe I had a problem in the endometrium and that’s why they didn’t come out. In my clinic, they have never said anything about the aspect of my endometrium. Could this be the problem for me to get pregnant?
Hello Natasha,
The aspect of the endometrium before doing a transfer is crucial for the embryo implantation, in the case that this does not have the right thickness (between 7-10 mm) decreases the chances of the embryo to implant correctly.
I recommend that you talk to your doctor to explain how your endometrium is and if this can be a factor in the non-achievement of your pregnancies.
In case they confirm that the endometrium in your case is adequate, you should look at different aspects such as the quality and viability of the embryo since it is possible that the correct implantation does not occur if there is not a good quality of gametes and consequently of embryos.
I hope I have helped you.
Best regards.
Hi, I have a 6mm endometrium and trilaminar, is it possible for me to get pregnant?
Hello MoonLight,
Experts recommend that for the correct implantation of the embryo, the endometrium should have a thickness between 7 – 10 mm, having 6 mm is at the limit below the recommended size.
If it has a trilaminar aspect and the indicated thickness, pregnancy is possible, although the probability of pregnancy is lower than it would be if the endometrium had an adequate thickness.
In the event that your endometrium does not achieve adequate thickness and you do not get pregnant, doctors can provide you with specific medication in order to thicken the endometrium.
I recommend that you read the following article: What’s the role of the endometrium, in which we explain what the endometrium is and its role in achieving pregnancy.
I hope I have helped you.
Best regards.