A system for recording, storing, and analyzing changes in a woman's basal body temperature, and displaying the analysis, comprising: (a) an intelligent, preprogrammed oral thermometer configured to compare a measured temperature with stored personal data of the woman and to display a status of the woman's fertility, the thermometer comprising: i. a microcontroller chip having a RAM, a ROM, a CPU, an ADC, and a voltage regulator, the chip having been pre-programmed with temperature detection software, bio-mathematical forecasting software, synchronization recognition software, and application communication software; and ii. a battery, an alarm, a display screen for displaying the results of the measurements and analysis done by the thermometer, means for connecting to a personal electronic device, and a tip which is designed to fit under a woman's tongue and which includes a temperature sensor; (b) application software configured to display the results of the measurements and analysis done by the thermometer on the display of a personal device connected to the thermometer, the personal device being a computer or a smart phone, wherein the system comprises means for entering personal data including menstruation data on the thermometer and, via the application software, on the personal electronic device, the thermometer and the application software on the personal electronic device comprise synchronisation means to exchange menstruation data and basal body temperature data; and the microcontroller chip of the thermometer is configured to process temperature measurement data and the personal data including menstruation data to display the fertility status. (a) an intelligent, preprogrammed oral thermometer configured to compare a measured temperature with stored personal data of the woman and to display a status of the woman's fertility, the thermometer comprising: i. a microcontroller chip having a RAM, a ROM, a CPU, an ADC, and a voltage regulator, the chip having been pre-programmed with temperature detection software, bio-mathematical forecasting software, synchronization recognition software, and application communication software; and ii. a battery, an alarm, a display screen for displaying the results of the measurements and analysis done by the thermometer, means for connecting to a personal electronic device, and a tip which is designed to fit under a woman's tongue and which includes a temperature sensor; i. a microcontroller chip having a RAM, a ROM, a CPU, an ADC, and a voltage regulator, the chip having been pre-programmed with temperature detection software, bio-mathematical forecasting software, synchronization recognition software, and application communication software; and ii. a battery, an alarm, a display screen for displaying the results of the measurements and analysis done by the thermometer, means for connecting to a personal electronic device, and a tip which is designed to fit under a woman's tongue and which includes a temperature sensor; (b) application software configured to display the results of the measurements and analysis done by the thermometer on the display of a personal device connected to the thermometer, the personal device being a computer or a smart phone, wherein the system comprises means for entering personal data including menstruation data on the thermometer and, via the application software, on the personal electronic device, the thermometer and the application software on the personal electronic device comprise synchronisation means to exchange menstruation data and basal body temperature data; and the microcontroller chip of the thermometer is configured to process temperature measurement data and the personal data including menstruation data to display the fertility status. wherein the system comprises means for entering personal data including menstruation data on the thermometer and, via the application software, on the personal electronic device, the thermometer and the application software on the personal electronic device comprise synchronisation means to exchange menstruation data and basal body temperature data; and the microcontroller chip of the thermometer is configured to process temperature measurement data and the personal data including menstruation data to display the fertility status.