Means for improving the success rate of pregnancy on the basis of blastocyst transfer is disclosed. The means comprises an agent for promoting pregnancy in blastocyst transfer comprising the supernatant of the culture which is obtained by culturing a human embryo in a medium until the embryo develops into a blastocyst. Also disclosed are a method for production of the agent, as well as a method for promoting pregnancy comprising； culturing a human embryo in a medium until the human embryo develops into a blastocyst, injecting a composition comprising the supernatant of the culture into the uterine cavity of a patient who is to undergo blastocyst transfer, and then transferring the blastocyst to the recipient.
