Basal Body Temperature Changes During Menstruation

Basal body temperature

During menstruation, is it true that the basal body temperature decreases? However, on the first day of my period, my basal body temperature was 36.85°C, on the second day it was 36.75°C, and on the third day it was 36.80°C.
What could be the reason for this? Is there any abnormality in my body? Thank you.

Mary, 30~39 year old female. Ask Date: 2022/03/30

Dr. Cai Yonglong reply Obstetrics and Gynecology

During menstruation, body temperature may slightly decrease, but this is not always the case.
If there are no discomforts, it is generally okay.
If you have any concerns, please visit a gynecologist.

Reply Date: 2022/03/30

More Info

Understanding basal body temperature (BBT) changes during menstruation is essential for tracking reproductive health and understanding the menstrual cycle. BBT is the body's temperature at rest, and it can fluctuate due to hormonal changes throughout the menstrual cycle. Typically, BBT is influenced by the phases of the menstrual cycle, particularly the luteal phase (after ovulation) and the follicular phase (before ovulation).

During the menstrual cycle, a woman's body experiences hormonal fluctuations, primarily due to estrogen and progesterone. After ovulation, progesterone levels rise, which usually causes an increase in BBT. This elevated temperature typically lasts until the onset of menstruation. When menstruation begins, progesterone levels drop, leading to a decrease in BBT. However, the exact pattern can vary from person to person.

In your case, you observed the following BBT readings during your menstrual period: 36.85°C on the first day, 36.75°C on the second day, and 36.80°C on the third day. These readings suggest a slight fluctuation but are generally within the normal range for BBT. It is important to note that BBT can vary due to several factors, including:
1. Individual Variation: Each woman's body responds differently to hormonal changes. Some may experience a more significant drop in BBT at the onset of menstruation, while others may see only a slight change.

2. Measurement Timing: BBT should be measured at the same time each day, ideally right after waking up and before any physical activity. Variations in measurement time can lead to fluctuations in recorded temperatures.

3. Environmental Factors: External factors such as room temperature, illness, stress, and even the method of measurement (oral, rectal, or vaginal) can influence BBT readings.

4. Hormonal Levels: The levels of estrogen and progesterone can vary significantly among individuals and even from cycle to cycle. If progesterone levels do not drop significantly at the onset of menstruation, BBT may not decrease as expected.

5. Health Conditions: While your readings do not indicate any immediate concern, underlying health conditions (such as thyroid disorders or hormonal imbalances) can affect BBT. If you notice persistent irregularities or have other symptoms, it may be worth consulting a healthcare provider.

In summary, the slight variations in your BBT during your menstrual period are not unusual and do not necessarily indicate a problem. However, if you have concerns about your menstrual cycle or any associated symptoms, it is advisable to consult with a healthcare professional, such as a gynecologist. They can provide a more comprehensive evaluation and address any specific health concerns you may have. Tracking your BBT over several cycles can also help you identify patterns and better understand your reproductive health.

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