Basal body temperature should be measured on which days of menstruation?

• A. Days 2, 3, and 4 of menstruation.
• B. Days 1, 2, and 3 of menstruation.
• C. Days 4, 5, and 6 of menstruation.
• D. Days 3, 4, and 5 of menstruation.

Answer: (A)

Tracking basal body temperature relies on a consistent, a.m. measurement taken before any activity to detect the small rise that indicates ovulation. To establish a reliable pre-ovulatory baseline, you start taking temperatures after the first day of your period and continue for a few days. Days two through four of the menstruation cycle are ideal because the temperature readings tend to be more stable and low during this early phase, giving you several consecutive data points to define your baseline. Once ovulation occurs, progesterone nudges the temperature upward, so having a clear baseline from days two to four makes the post-ovulatory rise easier to recognize. Measuring on later days or starting on day one can introduce variability that makes it harder to establish that baseline.