ObjectiveTo systematically evaluate the efficacy and safety of different low-molecular-weight heparins (LMWHs) in improving pregnancy outcomes in patients with recurrent abortion. MethodsThe PubMed, EMbase, Cochrane Library, CBM, CNKI, VIP and WanFang Data databases were electronically searched to collect randomized controlled trials (RCTs) related to the objectives from inception to July 2022. Two reviewers independently screened literature, extracted data and assessed the risk of bias of the included studies. Meta-analysis was then performed by using Stata 16.0 software. ResultsA total of 25 RCTs involving 4 631 patients were included. Enoxaparin, dalteparin, nadroparin, and tinzaparin were included. The results of network meta-analysis showed that the live birth rate of the tinzaparin was higher than that of enoxaparin and dalteparin. The live birth rate in nadroparin was higher than that in enoxaparin and dalteparin. The cumulative sorting probability showed that tinzaparin ranked best for improving the live birth rate, nadroparin ranked best for reducing the miscarriage rate, and enoxaparin ranked best for reducing the preterm birth rate. ConclusionCurrent evidence suggests that tinzaparin and nadroparin may be the best choice for improving pregnancy outcomes in patients with recurrent abortion. Due to the limited quality and quantity of the included studies, more high quality studies are needed to verify the above conclusion.