A method comprising: acquiring via a network biogas information representing a concentration of furfural of the user acquired by a sensor that detects the furfural discharged from a skin surface of the user； obtaining the reference information representing a lower limit of a normal range of the concentration of furfural per unit period of time, using a memory storing the reference information； and outputting information related to stress of the user an information terminal of the user, after it is determined that a frequency that concentration of the furfural of the user per the unit period of time is less than the lower limit of the normal range tends to increase, based on the biogas information acquired in a pregnancy period of the user.
