When we talk about fertility, much of the focus tends to be on the quality of the eggs, sperm and embryos. However, for a pregnancy to begin and progress, it is also essential that the site where the embryo is to implant provides the right conditions. The shape of the uterine cavity, the absence of any lesions inside it and the condition of the endometrium can all influence embryo implantation. For this reason, assessing what is known as the ‘uterine factor’ can provide important information in certain cases of infertility, implantation failure or recurrent miscarriages.
What is the uterine factor in infertility?
The uterine factor encompasses abnormalities of the uterus that may hinder embryo implantation or the development of the pregnancy. These may affect the shape of the uterus, its cavity or the endometrium – the tissue lining the inside of the uterus, into which the embryo must implant. Some cause symptoms such as abnormal bleeding, painful periods or pelvic discomfort, whilst others may go completely unnoticed. Furthermore, detecting a uterine abnormality does not necessarily mean that this is the sole cause of infertility: each finding must be interpreted within the context of the patient’s or couple’s full medical history.
What uterine problems can make it difficult to get pregnant?
Conditions that may affect the uterine cavity or the endometrium include the following:
Endometrial polyps
Endometrial polyps are generally benign growths of the endometrial tissue. Their impact on fertility depends, amongst other factors, on their size and location. When they distort the cavity or are situated in an area relevant to implantation, the specialist may consider removing them via hysteroscopy.
Fibroids affecting the uterine cavity
Fibroids are very common benign tumours, although not all of them affect fertility. Those that grow into the lining of the womb, known as submucosal fibroids, and some intramural fibroids that distort the uterine cavity are the ones that may have the greatest impact on implantation or pregnancy.
Uterine malformations
Some women are born with an abnormality in the shape of their uterus. There are different types, and not all have the same significance in terms of fertility. Three-dimensional ultrasound allows the uterine anatomy to be examined with great precision and, when an abnormality is detected, the medical team must assess its characteristics and the patient’s medical history before considering any intervention.
Intrauterine adhesions or Asherman’s syndrome
Intrauterine adhesions are bands of scar tissue that partially or completely bind the walls of the uterine cavity together. They can develop following surgery inside the uterus, particularly after procedures related to pregnancy, although they may also have other causes. Depending on their extent, they may be associated with very light or absent periods, difficulty conceiving, or pregnancy loss. Hysteroscopy allows them to be observed directly and, where indicated, treated with precision.
Chronic endometritis
Chronic endometritis is a persistent inflammation of the endometrium that often causes no specific symptoms. Its possible link to infertility, repeated implantation failures and recurrent miscarriages has been studied, although its prevalence varies depending on the population studied and the criteria used to diagnose it. In certain cases, it may be necessary to perform an endometrial biopsy and analyse the sample. If the diagnosis is confirmed, treatment should be tailored to each patient and their progress monitored as the specialist deems necessary.
Adenomyosis
Adenomyosis occurs when endometrium-like tissue grows into the muscular wall of the womb. It can cause heavy periods, menstrual pain or pelvic discomfort, although some women have no symptoms. Its potential impact on implantation and pregnancy should be assessed on a case-by-case basis and in conjunction with other reproductive factors.
Can a uterine abnormality occur without any symptoms?
Yes. A woman may have apparently normal periods and experience no discomfort, but still have an abnormality that is detected during an ultrasound scan or a hysteroscopy. This does not mean that all patients need to undergo every available test: the aim is to select the investigations that can actually provide relevant information in each individual case.
How are the uterus and the endometrium examined?
The examination usually begins with a medical history and a transvaginal ultrasound scan. Based on the results of these and the patient’s medical history, further tests may be recommended.
Transvaginal ultrasound scan
It is one of the key examinations in gynaecological and reproductive medicine. It enables the assessment of the uterus, the thickness and appearance of the endometrium, the ovaries and the possible presence of fibroids, polyps or other abnormalities.
Three-dimensional ultrasound scan
A 3D ultrasound scan provides a more comprehensive view of the external and internal structure of the uterus. It is particularly useful when a uterine malformation is suspected or when the uterine cavity needs to be examined in greater detail.
Histerosonografía
Hysteroscopy allows the inside of the uterus to be viewed directly using a very fine instrument fitted with a camera. It can be diagnostic or surgical and, in many cases, is carried out on an outpatient basis using small-calibre instruments. It also allows a lesion to be pinpointed and, where indicated, a sample to be taken or the lesion to be treated whilst avoiding damage to healthy areas of the endometrium. In our article on diagnostic hysteroscopy in assisted reproduction, we explain in greater detail what this procedure involves, how it is carried out and what information it can provide during a fertility assessment.
Endometrial biopsy
It involves taking a small sample of the endometrium for examination in the laboratory. It is not part of every fertility assessment, but it can be useful when there is a specific clinical suspicion, such as possible chronic endometritis.
When might a hysteroscopy be recommended as part of a fertility assessment?
Hysteroscopy does not need to be carried out as a matter of routine prior to any treatment or embryo transfer. The specialist may recommend it, amongst other situations, when:
- An ultrasound scan or hysterosonography reveals a possible abnormality within the uterine cavity.
- There is a history of polyps, submucosal fibroids, malformations or adhesions.
- There have been previous uterine procedures and the formation of scar tissue is suspected.
- Abnormal uterine bleeding occurs.
- There is a history of recurrent pregnancy loss.
- Implantation failures have occurred and medical assessment recommends examining the cavity in greater detail.
The final recommendation will always depend on the patient’s medical history, the tests carried out and the specific circumstances of each case.
What is the link between uterine factors and implantation failure?
Implantation is a complex process involving the embryo, the endometrium and the interaction between the two. An abnormality in the uterine cavity can hinder this process, but not all implantation failures are due to the uterus, nor do all the abnormalities found on their own explain why a pregnancy has not been achieved. When embryo transfers involving embryos considered viable have failed to result in pregnancy, the medical team reviews the case comprehensively: the patient’s age and medical history, the characteristics of the embryos, the transfer technique, the uterine anatomy and the condition of the endometrium, amongst other factors.
Can abnormalities of the uterine cavity be treated?
Many conditions can be treated, although not all require intervention. The decision depends on the type of lesion, its size and location, the symptoms, the patient’s reproductive history and the planned fertility treatment. Where indicated, surgical hysteroscopy allows for the targeted treatment of polyps, submucosal fibroids, septa and adhesions. The aim is not to treat every finding, but to identify those that may be clinically significant and to choose the most appropriate option for each patient.
Frequently asked questions about the uterine factor and fertility
Does a problem with the womb always lead to infertility?
No. Some abnormalities do not affect fertility, whilst others may only do so depending on their size, location or severity. The finding should be interpreted in conjunction with the rest of the reproductive assessment.
Does a normal ultrasound scan rule out all problems with the uterine cavity?
Not always. Some minor abnormalities or certain adhesions may require a hysterosonography, a 3D ultrasound scan or a hysteroscopy for further investigation.
Does a hysteroscopy hurt?
The experience may vary depending on the procedure and the individual patient. Many diagnostic hysteroscopies and some procedures are carried out in the doctor’s surgery using very fine instruments. If a more complex procedure is planned, the team will explain the most appropriate options for pain relief or anaesthesia.
Can chronic endometritis be detected by an ultrasound scan?
Not always. Where there is a justified suspicion, the specialist may recommend a hysteroscopy and/or an endometrial biopsy to complete the investigation.
Is a hysteroscopy necessary before in vitro fertilisation?
Not as a matter of routine. It may be indicated if previous tests show an abnormality, if there is a specific medical history, or if the course of the case suggests that the uterine cavity should be examined.
Written and medically reviewed by Dr Claudio Álvarez Pinochet
Medical Director – Gynaecologist specialising in reproductive medicine
