A Cochrane review [Abstract] 1 included 9 studies with a total of 1228 subjects. When studies at high risk of bias were excluded, anticoagulants did not have a beneficial effect on live birth, regardless of which anticoagulant was evaluated: Risk ratio (RR) for live birth in women who received aspirin compared to placebo was 0.94, (95% CI 0.80 to 1.11; n = 256), in women who received LMWH compared to aspirin RR 1.08 (95% CI 0.93 to 1.26, n = 239), and in women who received low molecular weight heparin (LMWH) and aspirin compared to no-treatment RR was 1.01 (95% CI 0.87 to 1.16; n = 322). Obstetric complications such as preterm delivery, pre-eclampsia, intrauterine growth restriction and congenital malformations were not significantly affected by any treatment regimen. In included studies, aspirin did not increase the risk of bleeding, but treatment with LWMH and aspirin increased the risk of bleeding significantly in one study.
A meta-analysis 2 assessed the effects of different treatments on live birth rates and complications in women with unexplained recurrent pregnancy loss. 21 RCTs regarding acetylsalicylic acid, low-molecular-weight heparin, progesterone, intravenous immunoglobulin or leukocyte immune therapy were included. No significant difference in live birth rate was found when acetylsalicylic acid was compared with low-molecular-weight heparin or with placebo. Meta-analyses of low-molecular-weight heparin vs. control found no significant differences in live birth rate (RR 1.47, 95% CI 0.83 to 2.61).
A randomized, double-blind, placebo-controlled trial 3 included 400 women with at least 3 consecutive first-trimester miscarriages. Live birth rate was 83.0% (n = 166) and 85.5% (n = 171) for the acetylsalicylic acid (75 mg) and placebo groups, respectively (P = 0.58). The difference was -2.5% (95% CI -10.1% to 5.1%). The risk ratio was 0.97 (95% CI 0.89 to 1.06).
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