Venous thromboembolism in pregnancy and the puerperium: incidence and additional risk factors from a London perinatal database

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. RESULTS: The 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 or = 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.