Objective To determine the incidence of venous thromboembolism in pregnancy and the puerperium and to identify risk factors for pregnancy-related venous thromboembolism.Design Cohort study and case±control study.Setting London, UK.Population 395,335 women with live births or pregnancies of 24 or more weeks of gestation between 1988 and 1997.Methods Data extraction from the St Mary's Maternity Information System database. Random sample of 5% for case±control study.Main outcome measures Incidence of venous thromboembolism; odds ratios for variables associated with venous thromboembolism. ResultsThe incidence of venous thromboembolism was 85/100,000 maternities. There were approximately twice as many postpartum as antepartum events. Blood group A, multiple pregnancy, caesarean section, cardiac disease, delivery at gestational age of ,36 weeks, a body mass index of $25, or more and maternal age of 35 or over were all found to increase incidence of venous thromboembolism. Conclusions Although venous thromboembolism is the leading cause of maternal deaths in the UK, it is still a rare event. Most of these events are deep vein thromboses occurring in the postpartum period. Antenatally multiple birth is an important risk factor. Postnatally women who have had a caesarean section, premature delivery or history of cardiac disease should be assessed carefully for venous thromboembolism.

Objective To determine the incidence of venous thromboembolism in pregnancy and the puerperium and to identify risk factors for pregnancy-related venous thromboembolism.

We believe that, before prescribing combined oral contraceptives, the venous as well as the arterial factors need to be considered and, in addition, age, obesity and smoking are all relevant when assessing an individual patient's risk.

Objective To compare the incidence of venous thromboembolism among women taking combined oral contraceptives before and after the October 1995 pill scare.

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