The science behind bleeding and clotting disorders in women and girls
Thrombosis and hemostasis are critical components of women and girls health, affecting blood clotting and bleeding processes throughout every stage of life. Women and girls face unique risks for bleeding and clotting disorders due to hormonal changes during menstruation, pregnancy, childbirth, hormone therapy and menopause, making specialized clinical knowledge and research essential for proper diagnosis, treatment and prevention of potentially life-threatening conditions. Click below to learn more.
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What is hemostasis?
Hemostasis is your body's natural ability to stop bleeding. When you're injured, your body activates a coordinated response: blood cells called platelets rush to the wound site and stick together, while special proteins in your blood (clotting factors) work to form a stable clot. This protective mechanism prevents excessive bleeding from cuts, injuries and even internal damage. Once the wound heals, your body breaks down the clot and blood flow returns to normal.
Understanding thrombosis
Thrombosis occurs when your blood clots form in the wrong place or at the wrong time - inside blood vessels where they shouldn't be. These unwanted clots can block blood flow to vital organs like the heart, lungs or brain, potentially causing serious complications like a heart attack, stroke or pulmonary embolism. Thrombosis represents the darker side of your clotting system: what happens when hemostasis goes too far.
Atrial Fibrillation (AFib) and its connection to bleeding and clotting
Atrial fibrillation (AFib) is the most common type of irregular heartbeat and can significantly increase the risk of blood clots and stroke. In AFib, the upper chambers of the heart do not beat normally, which can allow blood to pool and form clots inside the heart. If a clot travels to the brain, it can cause a stroke. The risk of AFib increases with age and may also be influenced by conditions such as high blood pressure, heart disease, diabetes and obesity. Women with AFib often experience different symptoms than men and may face a higher risk of stroke and complications.
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Managing AFib often involves balancing both clotting and bleeding risks. Many patients require blood-thinning medications (anticoagulants) to help prevent dangerous clots and strokes, but these treatments can also increase the risk of bleeding. This makes careful monitoring, individualized treatment decisions and ongoing communication between patients and healthcare providers especially important. Understanding AFib and its connection to both bleeding and clotting can help support earlier diagnosis, safer treatment and improved long-term health outcomes.
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Signs and symptoms of Atrial Fibrillation (AFib)
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Some people with atrial fibrillation (AFib) have no symptoms at all, while others may notice changes that come and go or worsen over time. Common symptoms can include:
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Rapid, fluttering or irregular heartbeat
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Heart palpitations or a racing heart
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Fatigue or unusual tiredness
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Shortness of breath
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Dizziness or lightheadedness
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Chest discomfort or chest pain
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Weakness or reduced ability to exercise
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Feeling faint or fainting
AFib is important to recognize because it can increase the risk of blood clots and stroke, even when symptoms seem mild. Women may experience more subtle symptoms, such as fatigue, weakness or shortness of breath, which can sometimes delay diagnosis. Anyone experiencing symptoms of AFib or signs of a possible stroke should seek medical attention promptly.
Bleeding and clotting: Two sides of the same system
Bleeding and clotting are two sides of the same biological process, one that must remain in careful balance to keep the body healthy. Women's hemostasis, the system that stops bleeding and prevents excessive clotting, relies on a precisely regulated chain of events involving platelets, clotting factors and blood vessel walls.¹
When this system tips too far in one direction, the consequences can be serious: too little clotting leads to uncontrolled bleeding, while too much raises blood clot risk in women across a range of conditions including venous thromboembolism (VTE). For women and girls, this balance is particularly complex, shifting with hormonal changes across the lifespan, during pregnancy and in the postpartum period.
Disruptions to women's bleeding and clotting can contribute to conditions as distinct as heavy menstrual bleeding and thrombosis in women, including life-threatening complications, such as maternal hemorrhage and pregnancy-related VTE.²
Healthcare resources for women and girls with bleeding disorders
Support by topic:
Resources for healthcare professionals on women's bleeding and clotting
The following resources are curated by subject and developed in collaboration with ISTH and its collaborative partners to support healthcare professionals, researchers and anyone working to improve care for women and girls with bleeding and clotting disorders. Resources include peer-reviewed articles, research papers, clinical guidelines and expert guidance. The ISTH Global Public Affairs Committee has vetted all resources to ensure accuracy, relevance and scientific integrity.
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Select a topic below to explore resources in that area. If you are a collaborative partner with resources you would like added to this collection, share them with us.
ACOG Committee Opinion: Screening and management of bleeding disorders in adolescents with heavy menstrual bleeding
American College of Obstetricians and Gynecologists
An official committee opinion from the ACOG with recommendations for screening and managing bleeding disorders in adolescents with heavy menstrual bleeding.
Venous thromboembolism in women with breast and gynaecological cancers: What do we know and what should we do?
Clinical and Applied Thrombosis/Hemostasis
A peer-reviewed article from Clinical and Applied Thrombosis/Hemostasis examining the current evidence and clinical recommendations for managing venous thromboembolism risk in women with breast and gynecological cancers.
CAT Guidelines: 2022 International clinical practice guidelines for the treatment and prophylaxis of venous thromboembolism in patients with cancer, including patients with COVID-19
ISTH
The 2022 international clinical practice guidelines provide evidence-based recommendations for the treatment and prevention of cancer-associated thrombosis, including considerations for patients with COVID-19.
Estrogen, progestin, and beyond: thrombotic risk and contraceptive choices
American Society of Hematology
An American Society of Hematology resource examining the thrombotic risks associated with estrogen and progestin-based contraceptives and guidance for supporting informed contraceptive decision-making in women with bleeding and clotting disorders.
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Deepen your understanding of bleeding and clotting disorders in girls and women from ISTH
Understanding the biological mechanisms behind bleeding and clotting disorders is essential to improving outcomes for women across all stages of life. From hormonal influences on coagulation to the unique hemostatic changes of pregnancy and menopause, the science is complex and continually evolving.
The ISTH Academy offers healthcare professionals, researchers and scientists a curated collection of courses and educational content designed to build and deepen expertise in thrombosis and hemostasis, with the clinical context needed to better recognize, diagnose and manage these conditions in women.
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ISTH clinical guidance and guidelines for girls' and women's health
The ISTH produces evidence-based clinical practice guidelines and guidance documents that provide practical recommendations for managing thrombosis and hemostasis disorders. Multidisciplinary expert panels develop these documents and address clinically important topics in girls' and women's health, offering informed guidance where randomized controlled trial data may be limited. Browse the ISTH's women's health guidelines and guidance documents below to support clinical decision-making across the reproductive lifespan.
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The ISTH provides comprehensive educational resources and peer-reviewed research publications to advance clinical practice in thrombosis, hemostasis, including girls' and women's bleeding and clotting disorders.
Access curated girls' and women's health content, continuing medical education (CME) through the ISTH Academy, and evidence-based research from our flagship journals on VTE, anticoagulation therapy and hemostatic disorders in women.
Additional resources from the ISTH
Journal of Thrombosis and Haemostasis (JTH)
Research and Practice in Thrombosis and Haemostasis (RPTH)
ISTH Academy
