Thromboembolism in Pregnancy: A Continuing Conundrum

Clinicians have known for years that pregnancy places women at increased risk for thromboembolism. In 1878, Angus MacDonald described pulmonary embolism and infarction in postmortem examinations of women dying during pregnancy and the postpartum period (1). He commented on the frequency of embolic events in women with cardiovascular disease who died. Our understanding of the pathophysiology and the natural history of thromboembolic disease in pregnant and postpartum patients has been expanding ever since 1856, when Virchow (2) postulated that hypercoagulability, vessel wall injury, and alterations in blood flow foster thrombus formation.

Since the observations of MacDonald and Virchow, the location, timing, and epidemiology of gestational and parturitional thromboembolism were largely in the realm of clinical impressions until our ability to diagnose hereditary and acquired thrombophilias enlarged our capacity to identify treatable patients at risk (3, 4). For the past 30 years, epidemiologic and molecular biologic studies have elucidated the complex relationship between pregnancy and thromboembolism. These studies have not substantially simplified the clinical management of pregnant patients, which would require clinical trials that are difficult to perform in a low-incidence illness.

The literature on managing thromboembolic states during pregnancy and the postpartum period has serious shortcomings. The main problem is that authors fail to adopt consistent case definitions (5-9). Authors must specify the patient's age, the timing of thromboembolic events during pregnancy or the weeks and months after delivery, the location of the thrombotic or embolic event, and the patient's history of thromboembolic disease or predisposition. Studies have failed to answer several important questions. What is the study sample? Women with first episodes of thromboembolism, women with repeated …