Incidence and risk patterns of venous thromboembolism in pregnancy and puerperium--a register-based case-control study.

OBJECTIVE: This study was undertaken to estimate the incidence of venous thromboembolism in pregnancy and puerperium and to identify risk factors for pregnancy-related venous thromboembolism.

STUDY DESIGN: A register-based case-control study with 613,232 pregnancies from 1990-2003 in 11 Norwegian counties. Medical records for eligible cases were revisited and relevant medical data were transferred to a specific case-report form. The diagnosis of venous thromboembolism was based on strict criteria. Data were analyzed by chi2 test and forward stepwise logistic regression.

RESULTS: In total, 615 cases were detected. The incidence of venous thromboembolism was 1 per 1000 pregnancies. The ante- and postnatal incidences were quite similar. Antenatal risk factors were assisted reproduction, gestational diabetes, age older than 35 years, multiple pregnancies, and primi-parity. Postnatal risk factors were cesarean section, preeclampsia, assisted reproduction, abruptio placenta, and placenta previa.

CONCLUSION: We found different ante- and postnatal risk patterns. Assisted reproduction and gestational diabetes were significant antenatal risk factors; whereas cesarean section and preeclampsia were strong postnatal risk factors.