In this webinar session, Dr Elena Santiago
, Fertility Specialist at Clinica Tambre, Madrid, explained what tests can be performed and what can be improved to increase the chances of successful embryo transfer.
Dr Elena Santiago started her presentation by explaining what she’d like to discuss during this webinar. She started with the definition of the endometrium. After that, she focused on different types of preparation for fresh embryo transfers and frozen embryo transfers. She finished by explaining the meaning of endometrial tests that can be done to see when it’s indicated or not.
The endometrium – definition
The endometrium is a tissue that we have inside the uterus, it is the innermost layer where the embryo implantation and the fetus development take place. This tissue is special in women’s organisms because it changes depending on the timing of the ovarian cycle. So there are different moments where we get different types of the endometrium, but everything is thought so that we can get pregnant. Due to the ovarian hormones produced during a natural cycle, the endometrium is changing. First, the oestrogens are the highest levels of hormones, and they help the lining to thicken for a potential pregnancy. Afterwards, we also need progesterone, which is produced after ovulation, and this hormone helps supply the lining and stimulates the glands to grow and nourish the early embryo. This is a very important part of a woman’s organism during her fertility treatment. There are different ways in which we can prepare the endometrium for an embryo transfer.
We can prepare the endometrium for a fresh embryo transfer during an IVF and for a frozen embryo transfer, in which there are 2 basic options of preparation. It can be during a substituted cycle with hormonal treatment, or sometimes we can also do a natural modified cycle.
Fresh embryo transfer – preparations
What are the requirements for a fresh embryo transfer to take place?
- 3 layer endometrium, more than 7 millimetres of thickness
- blood progesterone levels, less than 1 ng /ml the day of the trigger (if they are higher, it means that the window of implantation could be affected, and therefore, it’s not good to go ahead with fresh embryo transfer)
- no risk of having a Hyperstimulation syndrome (OHSS)
We shouldn’t proceed with fresh embryo transfer if, for example, we’ve been having loads of follicles growing during the simulations, more than 15 follicles of 16 millimetres on the day of the trigger, it’s better to freeze the embryo and do a transfer later on so that we don’t get that risk of hyperstimulation syndrome.
Also, hormones are going to help us to know if there is an added risk. So not only we are going to see the progesterone levels, but also the estrogen levels. If they are higher than 2,500 or 3000 pg/ml, it means that probably that woman has quite a risk of developing an OHSS syndrome afterwards when she gets pregnant, if the embryo implants.
Finally, we have to check the number of eggs that we retrieved because if we have more than 15 eggs, it’s better to freeze the embryo and go ahead with an embryo transfer at another cycle so that we get rid of the risk of OHSS.
Frozen embryo transfer – preparations
Nowadays, frozen embryo transfers are much more common than fresh embryo transfers. We are using PGT-A testing on the embryos, therefore, we need to freeze the embryos after the biopsy, so that we can wait for the results. There are different ways of preparing the endometrium.
- Substituted cycle
The first option will be with a substituted cycle. It’s the most common preparation used because it’s easier to plan, and we need fewer ultrasounds during the preparation.
We start with the oestrogens’ treatment from the start of a cycle, and this medication can be taken orally, transdermal with patches or creams or even vaginally. How does it work?
- 1st ultrasound at the start of the cycle (on the 2nd or 3rd day of the period to check if the ovaries are resting and that the endometrium is quite thin)
- start with oestrogens
- 2nd ultrasound to check the endometrial lining (a 3-layer of more than 7 millimetres of thickness) and check the progesterone level (lower than 1 ng/ml)
- add progesterone 5 days before the transfer (vaginally – 400 mg/ 12h) or subcutaneous progesterone (25 mg/12h)
If we are using the vaginal progesterone, it’s important that 1-to 2 days before doing the transfer, we check the progesterone levels again to see if they are correct. A lot of patients can get under 10 mg/ml levels of progesterone, which is considered not enough for proper embryo implantation or a developing pregnancy. Therefore, if we don’t have at least 10 ng/ml, we add subcutaneous progesterone to the vaginal one so that we are sure that our levels are going to be correct in a modified cycle.
2. Natural modified cycle
The steps in a natural modified cycle:
- the ultrasound, but from the 7th-8th day of the cycle onwards (each 48h-36h)
- a 3-layer endometrium of more than 7 millimetres, and the dominant follicle, have to be at least 16 mm so that we can schedule the transfer.
- hCG to produce ovulation and 7 days after the embryo transfer
- add progesterone 5 days before the transfer (if it’s vaginally, it is 400 mg//12h, every 12 hours, or subcutaneous progesterone 25 mg/24
The ovaries are also producing the progesterone on their own, so there is no reason to test progesterone levels with this type of protocol.
The pros & cons of using the natural modified cycle:
The pros are that we are going to use less medication, and oestrogens are not needed at this point, therefore, without the oestrogens, we can have fewer side effects.
It also has its cons, we can only use it in women with regular cycles. We are going to have less planification, which means the transfer will need to be scheduled. We also need to do more ultrasounds to follow up on the natural cycle, and there is more probability of cancellation due to spontaneous ovulation.
The endometrial tests are not necessarily done on every patient. It depends on the case, but some options allow us to look at the endometrium a bit more and have more information.
Endometrial receptivity (ERA, TIME tests)
The window of implantation is known as the period when the endometrium has the best conditions for the embryo implantation to occur. We say that the endometrium is receptive at that point. Normally, it lasts for around 3 days only. It should be more or less the same for each woman, but lots of research and lots of DNA testing of the endometrium showed that around 30% of the patients have a different window of implantation. Therefore, they will need to change their preparation protocol.
There are several tests that we can use. One of them is called the ERA test. Another one is called the TIME test. Both of them do the testing of numerous genes to see if the endometrium is at the point when we are doing the biopsy. If it is at the point, that means it is receptive.
We do preparation, no matter what type of protocol we use, but when we are going to do the embryo transfer, we are doing an endometrial biopsy, which is normally done at the consultation. Several days after, we get the results to see if this woman is receptive at that point, or if we need any changes in the protocol of preparations.
What are the indications for these tests?
- patients with several unsuccessful good quality embryo transfers
- patients with previous unsuccessful normal embryo transfer
- patients who want. to have a better approach to their endometrium before transferring their embryos
Endometrial microbiome (EMMA, ALICE, META tests)
We can do those tests at the same time as the endometrial biopsy. EMMA, ALICE and META tests are used to look at the microorganisms that we have inside the endometrium. It’s normal to have bacteria over there, but the normal bacteria that we require for implantation to take place and developing pregnancy to take place is called the Lactobacilli species. There are other good bacteria species there, but this is the basic one.
There could be pathogenic deviations in the dominant microbiome. If we don’t have that normal level of Lactobacilli required, the normal is more than 90% of this type of activity, we could have some infertility problems such as implantation failure or miscarriages. We can check this, it’s a DNA study of the bacteria we have inside our endometrium.
On the graph shown, in a patient with ongoing pregnancies, the population of Lactobacilli is completely dominant over the rest of the bacteria. In patients with recurrent miscarriages or implantation failures, there is also that type of bacteria, but other bacteria are coming out as the result of the DNA testing.
It’s not only going to tell us if our microbiome is fine, the same biopsy is going to tell us if there are any pathogens or bad bacteria that could be causing chronic endometritis. This is an infection that could be long term inflammation of the endometrium that doesn’t give any symptoms. If this occurs, we need to start an antibiotic treatment to try to stop the infection or inflammation.
When do we consider that we need to look at the microbiome?
- implantation failure
- recurrent miscarriages
- anyone who wants to have a better approach to the endometrium before the transfer
- thin endometrial lining
The endometrium is extremely important for fertility treatments. A good endometrium may increase the implantation rates. Apart from the basic examination regarding the lining of the thickness, we also have several endometrial tests that we can do to have much more information rather than only the ultrasound image. The main goal is to improve reproductive outcomes.