A method for diagnosing a risk for preterm delivery or miscarriage in a pregnant woman and preventing preterm delivery or miscarriage in the pregnant woman who has been determined to have the risk is provided. The method includes measuring plasminogen activator inhibitor-1 activity or level in plasma isolated from a pregnant woman. The method also includes determining that the pregnant woman has a risk for preterm delivery or miscarriage when the activity or the level is lower than that in the plasma of a normal pregnant woman. The method also includes administering plasminogen activator inhibitor-1 to the pregnant woman who has been determined to have the risk. A kit for the diagnosis of the degree of risk for preterm delivery or miscarriage also is provided. A pharmaceutical composition for the prevention of preterm delivery or miscarriage, comprising plasminogen activator inhibitor-1, also is provided.