A Simple Guide to Fibroids

Fibroids are non-cancerous growths that form around the uterus. They will affect up to one in three women over the course of their lifetime; however, only one third of these will experience symptoms. Women of African descent are up to three times more likely to develop fibroids. The most common symptoms are heavy periods, abdominal pain, lower back pain, pelvic pressure, constipation, increased frequency of needing to urinate and dyspareunia.

Types of fibroid

Fibroids are clinically classified according to their location:

  • Intramural – within the muscle wall of the uterus. This is the most common type.
  • Subserosal – project outside the uterus, into the pelvic cavity. These fibroids can be very large.
  • Submucosal – project into the cavity of the uterus.

When the fibroid is connected to the uterus with a stalk-like structure, it is known as a pedunculated fibroid. If the stalk twists it can cause additional symptoms of pain and nausea.

Fibroids range in size from resembling a pea, to being as large as a melon. They can also change size and shape over time. Most women find that when they go through the menopause their fibroids reduce in size and they experience symptomatic relief.

The impact of fibroids on fertility and pregnancy

Fibroids are detected in 5-10% of women with infertility and in 1-2% of cases they are the only abnormality found. Only fibroids that are intramural or submucosal have been shown to have a detrimental effect on fertility and cause complications during pregnancy.  If the fibroids are large and submucosal they can present a physical barrier to conception, preventing the sperm from reaching the egg, or impairing implantation. With regards to pregnancy, they can increase the risk of miscarriage, premature labour and undergoing a C-section. There is no definitive evidence that subserosal fibroids cause pregnancy complications.

The association between fibroids and hormones

Whilst the cause is unclear, fibroid growth seems to be dependent on oestrogen. In addition to diminishing in size with falling oestrogen levels during the menopause, they usually initially appear during a female’s reproductive years, when her oestrogen levels are high. Obesity is associated with higher oestrogen levels and a greater risk of developing fibroids and other disorders that can affect fertility, such as PCOS.

One of the factors providing greatest protection against fibroid development is childbirth, which reduces the risk by between 20-50%.  Having multiple children reduces this risk further. Exactly why giving birth reduces the risk of developing fibroids is unclear; proposed theories include altered hormonal status due to pregnancy and fewer menstrual cycles (you do not ovulate whilst pregnant), and structural remodelling of the uterus during and after pregnancy.

Taking the oral contraceptive pill might also reduce the risk of developing fibroids, although the available data is conflicting, with some studies suggesting no link. The injectable contraceptive, depot medroxyprogesterone acetate (DMPA), which contains a synthetic version of progesterone (progestin), has been shown to halve the risk of developing fibroids. Again the mechanism is unclear, but hypothesised to be due to progestin moderating the levels of oestrogen and thus reducing exposure of the uterus to excess oestrogenic activity.

Treating fibroids

Often discovered during routine pelvic investigations and confirmed using ultrasounds, fibroids may not require treatment at all. For the 60-70% of women who are asymptomatic, clinical monitoring will usually be sufficient. For those that do require treatment, medications and surgery are available, depending on the size and location of the fibroids, as well as the severity of the symptoms.

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  • “Fibroids.” NHS, www.nhs.uk/conditions/fibroids/. Page last reviewed: 17/09/2018.
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