OBJECTIVE： To observe therapeutic efficacy and safety of low-molecular-weight-heparin-sodium combined with dydrogesterone in the treatment of threatened abortion. METHODS： Medical information of 72 patients with threatened abortion were analyzed retrospectively and divided into control group （36 cases） and observation group （36 cases）. Control group was given Dydrogesterone tablet with initial dose of 40 mg， one day later every 12 h 10 mg/time. Observation group was additionally given abdominal subcutaneous injection of Low-molecular-weight-heparin-sodium injection 5 000 U， once a day， on the basis of control group. Both groups were treated for a week. Clinical efficacies of 2 groups were observed， and lumbar acid， vaginal bleeding， abdominal pain time， total treatment time， neonatal birth weight were also observed. The levels of hs-CRP， fibrinogen， D-dimer and platelet， the occurrence of ADR were observed before and after treatment. RESULTS： The total response rate of observation group was significantly higher than that of control group（91.7％ vs. 80.6％）， the backache， vaginal bleeding， abdominal pain time and total treatment time of observation group were significantly shorter than those of control group， the neonatal birth weight and gestational age of observation group were significantly more than those of control group， with statistical significance （P＜0.05）. Before treatment，there was no statistical significance in the levels of hs-CRP，fibrinogen，D-dimer and platelet between 2 group（P＞0.05）； after treatment， the levels of hs-CRP， fibrinogen， D-dimer and platelet in 2 groups were significantly lower than before， and the observation group was significantly lower than the control group， with statistical significance （P＜0.05）. There was no statistical significance in the incidence of ADR between 2 groups （P＞0.05）. CONCLUSIONS： Based on routine treatment， low-molecular-weight-heparin-sodium combined with dydrogesterone shows good therapeutic efficacy and safety for threatened abortion.