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.