Once the concentration of spermatozoa is inferior to 1 million/ml in two consecutive sperm samples taken three weeks apart. This level of concentration is obtained between 2 to 4 months of wearing the thermal ring. The 1 million/ml threshold was defined in 2007 for thermal, chemical and hormonal contraception methods. Below this threshold, you are considered contracepted.
Consequently, it is necessary to use another contraception method as long as the concentration of spermatozoa is higher than 1 million/ml.