The endometrium is the inner lining of the uterus where the embryo must implant. It plays a crucial role during the implantation process, allowing the embryo to begin forming the connections that will develop into the placenta.
Currently, we still lack full understanding of many mechanisms involved in this complex process, but little by little we are learning what is important for the embryo and the maternal endometrium to "communicate" effectively.
Frequently Asked Questions About the Endometrium
Endometrial preparation is a key part of assisted reproductive treatments, as it helps ensure good success rates and reduces the risk of miscarriage.
How is the endometrium prepared?
Endometrial preparation is carried out using medications that align with the ovarian cycle. Initially, the woman will need to take estrogens. The method of administration can vary — oral, patches, or creams — as well as the dosage.
Here we find two cases: women who achieve adequate endometrial growth with a low dose of estrogen, and others who will require higher doses to achieve proper growth.
It is important to individualize the treatment and adjust the dose to achieve adequate growth for each woman.
What is the ideal thickness of the endometrium?
When we talk about "growth," we are referring to the thickness of the endometrium, which is one of the decisive criteria for scheduling the embryo transfer.
At the start of endometrial preparation, after approximately 10–15 days of estrogen treatment, a monitoring ultrasound is performed to evaluate the endometrial thickness.
Traditionally, it is agreed that once the endometrium reaches a thickness of at least 7 mm, it is considered ready for transfer. However, this can vary from one patient to another.
It is, once again, essential to individualize each case and take uterine size into account when making an assessment, so the endometrial preparation can be tailored to each patient.
Endometrial structure
It is during ultrasound check-ups that we can assess the structure. In addition to size, it is essential for the endometrium to be homogeneous and trilaminar.
If polyps, submucosal fibroids, bleeding, or any complications arise during an endometrial preparation cycle, it is advisable to stop the cycle and address the issue in order to maximize the chances of pregnancy with the embryo transfer.
If a problem occurs during endometrial preparation, your doctor may recommend performing a hysteroscopy to evaluate the endometrium and uterine cavity. In cases where polyps or fibroids are present, it is recommended to remove them before proceeding with the embryo transfer.
What is the implantation window?
The concept of the implantation window refers to the days when the endometrium is receptive, allowing an embryo to implant.
Once progesterone is added to the endometrial preparation cycle, the embryo transfer must be performed at a precise moment, determined by the embryo’s development stage.
In some patients, the endometrial implantation window (the ideal moment for transfer) is displaced, and there are tests such as the ERA test that help determine the exact timing for the transfer.
Your doctor may adjust the dosage and number of days of progesterone administration to correct receptivity.
In any case, achieving an optimal endometrium for embryo transfer depends on factors such as:
- In patients with repeated implantation failure or recurrent miscarriage, further endometrial studies may be necessary to rule out conditions that could be reducing endometrial receptivity.
- It is important to follow a personalized treatment plan and endometrial preparation protocol for each patient in order to achieve an appropriate endometrium for transfer and increase the chances of pregnancy.
Book a free consultationDo you have any questions or need more information?
At Fertility Madrid, we specialise in treatments such as egg donation, in vitro fertilisation and artificial insemination, among others.
Please do not hesitate to contact our professionals at our fertility clinic and they will answer all your questions without obligation.
