Birth outcomes in pregnant women treated with low-molecular-weight heparin

Background. Pregnancy and puerperium are associated with an increased risk of venous thromboembolism. Low-molecular-weight heparin is the anticoagulant of choice in pregnant women because, unlike warfarin, it does not cross the placenta. However, there are limited data on the risk of adverse birth outcomes following use of low-molecular-weight heparin in pregnancy. Patients and methods. We performed a population-based cohort study to examine the safety of low-molecular-weight heparin use in pregnancy using data from the Pharmacoepidemiological Prescription Database, The Danish Medical Birth Registry and the Regional Hospital Discharge Registry in North Jutland County, Denmark. The birth outcomes in a cohort of 66 pregnant women treated with low-molecular-weight heparin between 1991-98 were compared with the birth outcomes of 17,259 pregnant women who did not receive any prescriptive drugs during pregnancy. Results. No increased risk of malformations, low birth weight or stillbirth was found. However, an increased risk of pre-term delivery was found (odds ratio: 2.11, 95% confidence interval: 0.96-4.65), which could reflect inherited thrombophilia as an indication of low-molecular-weight heparin. Conclusion. We have provided additional evidence of the safety of low-molecular-weight heparin use in pregnancy.