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 < 36 weeks, a body mass index 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.