Low-molecular-weight heparin did not provide any beneficial effect on pregnancy outcomes in patients with two or more implantation failures. Further trials are needed to confirm a trend in favor of low-molecular-weight heparin in the subgroup with women with three or more implantation failures. (Fertil Steril (R) 2011; 95: 2499-502. (c) 2011 by American Society for Reproductive Medicine.)