The objective is to find compounds which have an activity to improve the success rate of pregnancy and implantation in blastocyst transfer in mammals, to provide a method of producing and using the compounds, and to provide a pregnancy-promoting agent. Disclosed is a pregnancy-promoting agent containing one or more lysophosphatidic acids selected from the group consisting of LPA-C16:0, LPA-C16:1, LPA-C18:0, LPA-C18:1 and LPA-C18:2.