Use of propylene glycol to maintain the temperature of a portable case for storing at least one intrauterine catheter for embryo transfer. A portable case (1) for at least one intrauterine catheter that comprises a base body that includes a support with a recessed region, which adopts a form complementary to the general form of the intrauterine catheter and a lid connected to said base body, the support thereof including a thermostable medium, which consists of propylene glycol.