In assisted reproduction treatment there are two fundamental objectives in order to achieve a pregnancy which will go on to develop correctly.
The first objective is to have at least one embryo for the embryo transfer, and the second is to help the female achieve a receptive endometrium, meaning an endometrium that will be able to successfully accept an embryo and allow it to implant properly. Building off the second objective, today we are going to explain more about what we refer to as a refractory endometrium.
Embryo implantation is the process by which an embryo burrows into the surface of the endometrium. For this process to correctly take place, there needs to be a receptive endometrium, a properly functioning embryo in blastocyst stage and synchronisation between embryo development and endometrial lining development.
What is the endometrium?
The endometrial tissue, or the endometrium, is the inner-most layer which lines the inside of the uterus. Over the course of each menstrual cycle the endometrium undergoes significant changes which are crucial to supporting successful embryo implantation and, ultimately, conception.
What is a refractory endometrium?
It has been proven that endometrial thickness plays an important role in endometrial receptivity. It is measured and evaluated by performing a transvaginal ultrasound before the embryo transfer.
It is well-known that an endometrial lining with the correct appearance and thickness is associated with higher implantation and pregnancy success rates, especially when the lining measures more than 7 mm.
An endometrial lining measuring less than 7 mm has a direct relationship with lower success rates (implantation and pregnancy), in embryo transfer cycles, regardless of whether it was a fresh or frozen embryo transfer.
When the endometrium doesn’t reach a thickness of more than 7 mm even after using different treatments or therapies to promote its development, it is defined as a “refractory endometrium”.
The incidence of a refractory endometrium is between 0.7 and 2.5% of females undergoing assisted reproduction treatment.
Causes of a refractory endometrium
The root cause of a thin endometrium (<7 mm) cannot always be determined, and finding a solution that works is not possible in all cases.
Intrauterine adhesions caused by a prior surgical procedure are the most frequent cause of a refractory endometrium.
In over 90% of cases, these adhesions are the result of cervical dilation and curettage (D&C) performed following a miscarriage. Other causes include uterine procedures such as fibroid removal or endometrial ablation.
Radiotherapy can also lead to a refractory endometrium, as can endometrial infections such as endometritis. Congenital uterine abnormalities could also be to blame.
In many cases, a cause cannot be determined and it is considered an idiopathic pathology, meaning spontaneous in origin.
How is a refractory endometrium diagnosed?
2D and 3D vaginal ultrasounds, hysterosonograms and hysteroscopy are the main tools used to diagnose a refractory endometrium.
What solutions are available for a refractory endometrium?
In addition to treating the root cause, if one has been pinpointed, there are different alternatives when it comes to trying to improve the patient’s endometrial thickness such as prescribing a higher dose of the hormone oestrogen, as well as having the patient take it for a longer amount of time (here we explain what type of hormones we use in fertility treatment). The administration route of oestrogen can also be changed (i.e. it can be taken orally, vaginally and/or applied to the skin).
Another option would be to cancel the embryo transfer, freeze the embryos and delay transferring any embryos until a cycle in which the endometrial lining has reached a better thickness (here you can see how a frozen embryo transfer works).
A frozen embryo transfer can be carried out two different ways: either in a natural cycle, or in a medicated cycle. In some patients, endometrial thickness is better in a natural cycle due to the effects of natural oestrogen production.
Although the points mentioned above are the main treatments used in patients diagnosed with a refractory endometrium, other types of additional treatments for improving endometrial thickness have been noted such as the use of pentoxifylline, aspirin, vitamin E, sildenafil and the intrauterine administration of platelet-rich plasma (PRP).
Is pregnancy possible if I’ve been diagnosed with a refractory endometrium?
Although it is true that adequate endometrial thickness increases the odds of conceiving, there is no endometrial thickness for which achieving a pregnancy is impossible.
In fact, there have been reports of pregnancies that were achieved in patients whose endometrial thickness measured as low as 4 mm.
We hope we’ve been able to answer all your questions concerning the refractory endometrium in assisted reproduction. At URE Centro Gutenberg we’re here for you, so if you still have questions you simply need to request an appointment with us and we’ll clarify any additional doubts at a cost-free initial consultation.
