A nurse is teaching a client about family planning using the basal body temperature method. Which of the following instructions should the nurse include in the teaching?

A. "Take your temperature every night before going to bed." Basal body temperature (BBT) must be measured after a full night’s sleep, not at bedtime, to accurately detect ovulatory shifts in temperature. B. "Take your temperature 1 hour after getting out of bed." Delaying the measurement even by an hour can alter the results, as physical activity and environmental exposure can cause inaccurate readings. C. "Take your temperature immediately after waking and before getting out of bed." This is the correct instruction. BBT should be taken at the same time each morning, right after waking, before any activity, to detect the slight rise in temperature (0.3–0.6°C or 0.5–1.0°F) that typically follows ovulation. D. "Take your temperature within 30 minutes after your first morning void." Waiting until after voiding can also affect the reading. The temperature should be taken prior to any physical movement, including going to the bathroom, for best accuracy.