Reliability of Urine Temperature as a Measurement of Basal Body Temperature

Natural family planning is based on the recognition of physiologic signs and symptoms that identify fertile and infertile phases of the menstrual cycle. Identification of the onset of the infertile period can be determined when the upward shift in basal body temperature (BBT) has occurred. A study was conducted to determine if the temperature of the first-morning voided urine adequately represents BBT. In 22 subjects, vaginal temperature, taken immediately upon awakening, was compared with first-morning voided urine temperature as measured continuously by thermocouples mounted in either of two flow-through devices attached to a toilet bowl. A significant correlation was found between the two temperatures. The convenience and hygiene of the method together with the reliability of urine temperature as an estimator of BBT could reduce the generally high rate of noncompliance of women choosing this natural method of family planning.