Uterine fibroids, also known as leiomyomas, are non-cancerous muscular growths that develop within or on the wall of the uterus. These growths are common, affecting many women during their reproductive years, though many never experience symptoms. The physical presence of fibroids can lead to various complications, including concerns about blood clots. This article explores the two distinct ways fibroids relate to clotting: the common issue of large clots during menstruation and the less frequent, but more serious, risk of systemic blood clots.
The Common Effect: Clotting During Menstruation
The most frequent scenario involving fibroids and blood clots occurs locally within the uterus during a menstrual period. Fibroids, particularly those classified as submucosal because they bulge into the uterine cavity, significantly increase the surface area of the uterine lining. This enlargement leads to a much heavier volume of blood loss, a condition medically termed menorrhagia.
The uterus manages menstrual flow by releasing anticoagulation factors, chemicals designed to keep blood liquid for easy passage. However, when bleeding is exceptionally heavy or the blood is expelled too quickly, these natural anticoagulants become overwhelmed. Consequently, the blood clots before leaving the body, resulting in the visible passage of large, dark, gelatinous masses.
The presence of fibroids can also interfere with the normal muscular contractions of the uterus. These contractions are necessary to constrict blood vessels and control bleeding once the lining is shed. This impaired ability to contract efficiently contributes to the prolonged and heavy flow, further exacerbating the formation of large menstrual clots.
The Systemic Risk: Fibroids and Venous Thromboembolism
A less common but more serious complication associated with fibroids is the potential for systemic clotting, known as Venous Thromboembolism (VTE). VTE includes Deep Vein Thrombosis (DVT), the formation of a clot in a deep vein, usually in the leg or pelvis. If a piece of this clot travels to the lungs, it causes a life-threatening Pulmonary Embolism (PE).
The primary mechanism linking fibroids to this systemic risk is mechanical compression. Extremely large fibroids can grow to a size that exerts physical pressure on major blood vessels in the pelvis and abdomen. This compression can restrict blood flow in the pelvic veins, including the iliac veins and, in some cases, the Inferior Vena Cava (IVC), which is the body’s largest vein.
This external pressure leads to venous stasis, meaning blood flow slows down significantly. Slowed blood flow is a major component of Virchow’s triad, a set of factors that promote VTE formation. The left iliac vein is frequently affected due to its anatomical course, which can account for a higher incidence of left-sided DVT in patients with large fibroids.
Beyond mechanical compression, there are other potential contributing factors, though they are less understood. Chronic heavy bleeding from fibroids often results in iron deficiency anemia. Some research suggests that severe anemia may, paradoxically, be associated with a state of hypercoagulability, or increased clotting tendency, which could heighten the systemic VTE risk.
Surgical procedures used to treat fibroids, such as myomectomy or hysterectomy, carry a standard VTE risk associated with major surgery. The presence of fibroids, particularly a large uterine weight of 250 grams or more, is independently associated with increased odds of VTE both before and immediately after intervention.
Recognizing Symptoms and Mitigating Risk
Recognizing the signs of systemic clots is important for timely intervention. Symptoms of a DVT typically include swelling, pain, tenderness, or a feeling of warmth in one leg, particularly the calf or thigh. If the clot has traveled to the lungs, a PE may cause sudden shortness of breath, chest pain that worsens with a deep breath, or a rapid heart rate.
The most effective way to mitigate the systemic clotting risk associated with fibroids is by managing the size and impact of the fibroids themselves. Reducing the bulk of the fibroids, through medication or interventional procedures, can relieve the mechanical compression on the pelvic veins.
Individuals with large fibroids or those undergoing surgery should consult with their healthcare provider to discuss appropriate screening and prophylactic measures. Managing heavy menstrual bleeding is also important to address the underlying anemia that may contribute to a pro-thrombotic state. A comprehensive approach involves regular monitoring of fibroid growth and addressing any new or worsening symptoms promptly.