Duration of labor among women with thromboembolic events: A Swedish register study

INTRODUCTION: Inflammation is central to initiation of labor and coagulation is closely interlinked with inflammation. Low-molecular-weight-heparin (LMWH) promotes inflammatory cervical remodeling, myometrium contractility and has been associated with shorter duration of labor. MATERIAL AND METHODS: This was a cohort study of 136,661 deliveries 2013–2017, identified in the Swedish Pregnancy Register with prospectively collected pregnancy and labor characteristics. Information of duration of labor was retrieved from the electronic birth records and analyzed with Cox proportional hazard regressions according to previous or current thromboembolic disease (overall) with or without LMWH treatment with non-exposed as reference. RESULTS: The crude hazard ratio for vaginal delivery was not different between women with thromboembolic disease and women without thromboembolic disease (HR 0.99, 95 % CI 0.91–1.09). A lower hazard ratio for vaginal delivery was observed among women with venous thromboembolism (VTE) with concomitant LMWH use/treatment (adjusted HR 0.86, 95 % CI 0.76−0.98) compared to non-exposed, implying a longer duration of labor in these cases. CONCLUSION: Thromboembolic disease was not associated with shorter duration of labor and in presence of LMWH these women experienced longer duration of labor.