Doring, G.K. (1967). Uber die zuverlassigkeit der temperaturmethode zur empfangnisverhutung. [Reliability of the temperature method as a means on contraception]. Deutsche Medizinische Wochenschrift, 92, 1055-1061.
125 unwanted pregnancies occurred during the period of observation (3.1 failures per 100 application years, according to Pearl’s formula). 307 women used a strict form of temperature guidance for 11,352 cycles (only the period from the third day of the hyperthermic phase to the following menstruation were taken as unfertile). The failure rate here was 0.8 per 100 years.
“It is concluded that strict observation of the temperature method as a means of contraceptive control gives results similar to those obtained by using ovulation-inhibitory drugs.”
Some natural drawbacks of this method are that infection can cause premature temperature increase, and the ovulation cycle may be irregular naturally or because of medication.