Evaluation of the effect of low molecular weight heparin in unexplained recurrent pregnancy loss: a meta-analysis of randomized controlled trials

Introduction The effectiveness of low molecular weight heparin (LMWH) in preventing miscarriage of unexplained recurrent pregnancy loss remains controversial. In order to explore the effect of LMWH therapy in unexplained recurrent pregnancy loss, we conducted this meta-analysis. Methods We searched four databases PubMed, Cochrane Library, EMBASE, and Clinical Trials.gov (up to February 2020) for the randomized control trials (RCTs) evaluating the effectiveness of LMWH on the treatment of recurrent miscarriage. We used Stata software to perform a meta-analysis. Moreover, we performed analyses of sensitivity and predefined subgroups based on the definition of recurrent miscarriage (e.g. 2 or more miscarriages or 3 or more miscarriages) to search the source of heterogeneity. Results 5 studies met the selection criteria, involving 1452 participants. LMWH reduce the risk of miscarriage of women suffering >= 3 miscarriages (RR = 0.46; 95% CI = 0.35-0.61, p = .00), but the risk of miscarriage of women suffering >= 2 miscarriages was not decreased by LMWH (RR = 0.70; 95% CI = 0.57-0.86, p = .26). No substantial influence was found on Live birth rate (RR = 1.19; 95% CI = 0.99-1.43), Preterm birth (RR = 0.95; 95% CI = 0.65-1.38), Preeclampsia (RR = 0.89, 95% CI = 0.45-1.76), Small for gestational age (RR = 0.89; 95% CI = 0.64-1.51). Conclusion LMWH treatment may decrease the miscarriage rate in women suffering a history of 3 or more miscarriages, but not reduce the incidence of miscarriage in women suffering a history of 2 or more miscarriages. We need more RCTs to provide robust and reliable results.