Introduction

Uterine fibroids are common non-cancerous tumours found in the uterus.¹ The majority are under 2 cm, but some can grow as large as 50 cm.^2,3 They develop in around 70% of people assigned female at birth (AFAB), usually at a reproductive age; however, not all are symptomatic.⁴ Those that are symptomatic can develop a range of gynaecological symptoms, one of which is difficulty conceiving and maintaining a pregnancy, otherwise known as infertility. 

Overview of fertility and conception

In the reproductive system of people AFAB, the uterus is what is known as the womb. It is an 8 cm long organ behind the bladder, and is where pregnancy takes place. The uterus consists of three layers:⁵ 

• Endometrium: the innermost layer that grows and sheds during the menstrual cycle
• Myometrium: smooth muscle layer that grows during pregnancy and contracts during childbirth 
• Perimetrium: the outermost layer that covers the entire uterus 

At approximately day 14 of the menstrual cycle, one ovary releases an egg, which travels through the fallopian tube.⁶ Fertilisation occurs when a sperm cell fuses with the egg and their nuclei merge to form a zygote, which quickly divides and begins to develop into an embryo.⁷ The embryo then travels into the uterus and implants into the endometrium of the uterine wall, establishing pregnancy. Both fertilisation and uterine wall implantation must occur for a successful pregnancy.

Types and locations of fibroids

There are 3 main types of fibroids, categorised based on their location.⁸ They are further grouped as pedunculated or non-pedunculated, which refers to whether or not the fibroid is attached to the uterus by a stalk. The 3 types are: 

• Subserosal: fibroids that grow outwards and stick out on the surface of the uterus, into the pelvis
• Intramural: in the myometrium
• Submucosal: fibroids that grow under the endometrium from the myometrium and bulge out into the uterine cavity                                                                                                       

How fibroids affect fertility

Uterine fibroids are believed to be responsible for infertility in 2-3% of people AFAB struggling to conceive. However, it is important to highlight that not all of them with uterine fibroids are infertile.⁹ Infertility is the inability to conceive and have a successful pregnancy following one year of unprotected sexual intercourse. In the case of uterine fibroids, this can occur for a number of reasons, depending on the location, size and number of fibroids.¹⁰ Some of those reasons are: 

• Mechanical blockage of fallopian tubes: the outgrowth of uterine fibroids can compress the fallopian tube so that the sperm cannot enter and fuse with the egg¹⁰
• Preventing implantation of the embryo into the uterine wall: submucosal fibroids can disrupt the junction between the endometrium and myometrium, which can reduce the chances of embryo implantation
• Altered uterine blood supply: uterine fibroids can alter the blood supply in the endometrium, decreasing the chance of embryo implantation¹⁰
• Issues during pregnancy: uterine fibroids have been associated with an increased risk of miscarriages, prematurity and placental complications¹⁰
• Distortion of uterine shape: the appearance of fibroids changes the uterine shape and reduces the chance of successful pregnancy because it is a disadvantage for embryo plantation and growth, as it is more difficult¹⁰
• Release of hormones: fibroids can release or cause the release of hormones, which can interfere with the release of the egg into the fallopian tube, sperm transport and embryo implantation¹¹

Risk factors 

Some factors that increase the risk of developing uterine fibroids are:¹²

• Black race
• Premenopause
• Family history of previous uterine fibroids 
• Early menarche (first period > 11 years old)
• A diet low in vegetables and fruit
• Low vitamin D
• Processed and preserved foods 
• Alchohol consumption
• Obesity
• High blood pressure

Symptoms

20-25% of people AFAB experience clinician symptoms when having uterine fibroids.⁴ The most common are related to painful, heavy and irregular periods. Some also complain of prolonged and increased frequency of periods. The fibroids are also heavily associated with pain and pressure symptoms, including chronic pelvic pain, abdominal pain and pain during sexual intercourse. Depending on the size and site of the fibroids, they can also put pressure on the bladder.¹³ 

Diagnosis 

Clinical examination 

A clinician may examine the pelvis, which may reveal an enlarged or distorted uterus and abnormal masses. There may be signs of anaemia in patients experiencing frequent and heavy periods, such as nail changes and pale skin and eyes (pallor).¹¹ 

Imaging 

Ultrasound

Ultrasound scanning is the preferred initial imaging method for uterine fibroids, due to being relatively non-invasive, safe, readily available and low cost.⁴ The preferred method is usually transvaginally, whereby the probe is placed into the vagina to view the uterus from below. However, there is the option to scan the uterus through the abdomen or the rectum if the patient feels too uncomfortable. 

Hysteroscopy

To view the inside of the uterus, a hysteroscopy is carried out. A long thin tube with a light and camera on the end, known as a hysteroscope, is fed through the vagina and up the cervix to visualise the uterus and any underlying uterine fibroids. It is usually carried out between the first week of the menstrual cycle, when the endometrium is still thin. The procedure is generally safe, but there is a risk of infection and injury to the uterus. 

Magnetic resonance

In complex cases, magnetic resonance imaging (MRI) is used to obtain high-resolution imaging of uterine fibroids. This method is safe as it is non-invasive and does not use any radiation. However, it can be expensive, and there may be waiting times for appointments. MRIs can take detailed images of the uterus to determine the exact size and location of fibroids, even the smallest ones.⁸

Treatment options and fertility

Medical treatments

First-line treatment is usually to control symptoms such as abdominal pain and heavy, irregular periods.¹⁴ Non-steroidal anti-inflammatories, tranexamic acid, and hormonal treatments, such as combined oral contraceptives and hormonal coils, aim to regulate periods and reduce the volume of blood lost during each menstrual cycle. Hormonal therapies, such as injection of gonadotropin-releasing hormone analogues (GnRHas), have also been shown to be effective at reducing the size of fibroids, which can also reduce the incidence of other symptoms, such as pressure. 

Surgical treatments

Myomectomy is a surgical procedure in which the fibroids are removed, but the uterus is preserved to increase the chances of fertility. Depending on the size and location of the fibroids, there can be varied surgical approaches including via the abdomen or the vagina and cervix. The smaller a fibroid is, the easier it is to remove and the higher the chance of uterine preservation. As a result, many patients will undergo hormonal therapies to reduce the size of their fibroids before a surgical procedure.¹⁴ 

This procedure has been shown to significantly improve fertility in people AFAB trying to conceive, with 25-77% having successful pregnancies following myomectomy.¹⁵ However, it is important to note that the resurgence of uterine fibroids is a possibility after successful removal. 

Assisted reproductive techniques

In cases where conception is still difficult despite treatment, in vitro fertilisation (IVF) may be an appropriate intervention.¹⁶ Briefly, an egg is fertilised by a sperm in a laboratory, and the resulting embryo is transferred and implanted into the uterus. IVF has been found to be successful in people AFAB with uterine fibroids, particularly those with fibroids smaller than 4 cm, meaning it can be a suitable option for those who struggle with infertility. 

Summary 

• Uterine fibroids are common, benign tumours that originate in the uterus and can affect fertility 
• Fertility is the inability to conceive and maintain a normal pregnancy, after at least 12 months of unprotected sexual intercourse
• Uterine fibroids affect fertility by preventing sperm fertilisation of the egg or implantation of the embryo
• Common symptoms usually manifest as abdominal pain and heavy and irregular periods 
• Different imaging techniques can be used for diagnosis, such as MRI, ultrasound and hysteroscopy
• Treatments include hormonal medication, pain relief and surgical interventions to improve symptoms and increase fertility 
• In vitro fertilisation is a suitable intervention for women struggling with infertility, particularly those with smaller fibroids