What Causes Pulmonary Embolism in Pregnant Women?
Understanding the Risk of Pulmonary Embolism During Pregnancy
Pregnancy is a transformative period that brings about numerous physiological changes in a woman's body. While many of these changes are natural and necessary for supporting fetal development, some can inadvertently increase health risks—among them, pulmonary embolism (PE). This potentially life-threatening condition occurs when a blood clot travels to the lungs and blocks a pulmonary artery. Although relatively rare, PE is one of the leading causes of maternal mortality worldwide, making it crucial to understand its underlying causes and risk factors.
Hypercoagulable State: The Body's Natural Clotting Response
During pregnancy, the body naturally shifts into a hypercoagulable state—a condition where the blood is more likely to clot. This evolutionary adaptation helps minimize blood loss during childbirth. However, it also increases the risk of abnormal clot formation. Levels of several clotting factors, including fibrinogen, rise significantly throughout gestation. Elevated fibrinogen enhances blood viscosity and promotes clot stability, creating an environment conducive to thrombosis. This heightened coagulation activity begins in the first trimester and continues through the postpartum period, peaking shortly after delivery.
Physical Pressure from the Growing Uterus
As the uterus expands to accommodate the growing fetus, it exerts increasing pressure on surrounding organs and blood vessels—particularly the inferior vena cava, the large vein responsible for returning deoxygenated blood from the lower body to the heart. This mechanical compression slows venous return, leading to blood stasis in the legs and pelvic region. Prolonged pooling of blood not only increases pressure within the veins but can also damage the endothelial lining of blood vessels. Once the vascular wall is compromised, platelets and clotting proteins are more likely to accumulate, initiating the formation of deep vein thrombosis (DVT), a primary precursor to pulmonary embolism.
Hormonal Changes and Vascular Function
Pregnancy involves significant hormonal fluctuations, especially elevated levels of progesterone. While essential for maintaining pregnancy, progesterone induces relaxation of smooth muscle tissues—including those in the walls of veins. This vasodilation reduces venous tone and contributes to sluggish blood flow, particularly in the lower extremities. Combined with gravitational effects and reduced mobility, this slow circulation fosters venous stasis, further elevating the likelihood of clot development in the deep veins of the legs or pelvis.
Additional Risk Factors That Amplify Threats
Beyond the physiological changes inherent to pregnancy, several external and personal factors can dramatically increase the risk of pulmonary embolism. Advanced maternal age (typically over 35), obesity, and a history of thromboembolic disorders are well-documented contributors. Other high-risk conditions include preeclampsia, cesarean delivery, prolonged immobility (such as bed rest or long-haul travel), and multiple pregnancies (e.g., twins or triplets).
How Clots Travel to the Lungs
The vast majority of pulmonary emboli originate as deep vein thromboses in the lower limbs or pelvic region. When a portion of the clot breaks loose, it enters the systemic circulation, moving through the right side of the heart and into the pulmonary arteries. Once lodged in a narrowed vessel, the clot obstructs blood flow, impairing oxygen exchange and potentially causing sudden shortness of breath, chest pain, or even cardiovascular collapse. Early detection and preventive strategies—such as compression stockings, anticoagulant therapy when indicated, and regular movement—are vital for at-risk individuals.
Prevention and Awareness Are Key
While pulmonary embolism poses a serious threat during pregnancy and the postpartum phase, many cases are preventable with proper medical oversight. Healthcare providers often assess thrombotic risk early in prenatal care, especially for women with known risk factors. Education, lifestyle modifications, and timely interventions play a critical role in safeguarding maternal health. Expectant mothers should be encouraged to stay active, maintain hydration, and report any symptoms such as leg swelling, unexplained shortness of breath, or sharp chest pain without delay.