Does Low Molecular Weight Heparin Shorten Term Labor?

Clinical experience has fostered the belief among some clinicians that women who receive low molecular weight heparins (LMWHs) are less likely to have protracted labor and therefore, less likely to require operative delivery. Previous studies have identified changes in the uterine and cervical extracellular matrix of heparan sulfate proteoglycans in normal and protracted labor. These changes and clinical observations suggest that LMWHs may influence the parturition process and shorten delivery time. This retrospective study investigated the effects of LMWHs on parturition time in pregnant women with a history of thrombotic disorders. The study subjects were 99 nulliparous pregnant women who had been treated with an LMWH (dalteparin) because of a history of previous venous thromboembolism, thrombophilia, or an acute venous thromboembolism during the current pregnancy. The women had been treated for 1 to 6 months before delivery. The control group was comprised of 198 untreated healthy nulliparous women with spontaneous onset of labor matched according to age and parity. The study and control groups were compared with respect to labor time, proportion of operative deliveries, and neonatal outcomes. Among women who had a spontaneous vaginal delivery, labor time was significantly shorter in those treated with dalteparin than in the untreated controls (6 vs. 9 hours, P < 0.0001). The number of operative deliveries was the same in the dalteparin and control groups, but the dalteparin-treated women required fewer operative interventions due to protracted labor (P = 0.0014). There was no difference in neonatal outcome between the groups. These findings suggest that LMWH therapy is associated with shorter labor time and a decreased number of operative interventions for protracted labor.