A retrospective study on the use of low-molecular-weight heparin for prevention of pregnancy-related recurrent venous thromboembolism and obstetrical complications

Background: The risk of venous thromboembolism (VTE) is increased during pregnancy and it is further increased together with pregnancy complications in women with personal history of VTE and thrombophilia abnormalities. It is unclear how the use of low-molecular-weight heparin (LMWH) may prevent such complications. Objective: To evaluate the potential benefits and risks of the use of LMWH for prevention of pregnancy-related VTE and obstetrical complications in the first pregnancy after a previous VTE. Methods: This retrospective cohort study includes fertile women referred to the Thrombosis Center from January 2000 to September 2018 for a thrombophilia work-up, after having had at least one previous VTE and one pregnancy thereafter. Data on pregnancy-related recurrent VTE, pregnancy outcomes and the use of LMWH were collected. Results: Among 208 women, no thrombosis or major bleeding was recorded in 138 pregnancies conducted with LMWH, whereas 10 VTE (14%) were recorded in 70 pregnancies conducted without. Nine women (90%) with recurrent VTE had had a previous hormone-related event. The incidence of miscarriage was lower in pregnancies with LMWH than in those without (11% vs. 26%, relative risk 0.4, 95% confidence interval: 0.2-0.8), whereas late obstetrical complications and terminations were similar in the two groups. The prevalence of terminations was doubled in women with thrombophilia (12%) than in those without (6%). Conclusions: LMWH prophylaxis during pregnancy appears to be effective and safe for the prevention of recurrent VTE and may reduce the incidence of miscarriage.