What is covered in this article?
- Defining Basal Body Temperature (BBT) charting
- Importance of tracking the BBT for women’s fertility
- The timing and symptoms of ovulation
- How to properly chart the BBT across the menstrual cycle and factors effecting BBT results
- Chinese medicine considerations for BBT charting and fertility
What is BBT?
Basal body temperature (BBT) charting is a simple, non-invasive method used to monitor a woman’s body temperature during the menstrual cycle. By recording the body’s temperature at rest, typically first thing in the morning, we can gain valuable insights into ovulation patterns, hormonal changes, and potential fertility status. This article will explore the basis for BBT charting, its application in assessing ovulation for fertility, and conditions such as hypothyroidism, polycystic ovarian syndrome (PCOS) and endometriosis. Additionally, we will discuss the perspective of Chinese Medicine in relation to BBT charting and regulating the menstrual cycle for the purpose of fertility.
BBT charting in women’s health & hormones
BBT charting relies on the principle that a woman’s basal body temperature fluctuates in response to hormonal changes throughout her menstrual cycle. BBT can be an effective tool by confirming when ovulation has occurred [1]. It can also be used to determine the length of the luteal phase, give clues into thyroid function, assess how stress and lifestyle factors are effecting the cycle, and potentially assist with the diagnosis of PCOS and endometriosis. In order to understand things a little better, we should briefly cover the different stages of the menstrual cycle, which include menstruation, the follicular phase, ovulation, and the luteal phase. From here we’ll then delve into the relevance of BBT for fertility.
A quick breakdown on the menstrual cycle
During the follicular phase (pre-ovulation), Follicle Stimulating Hormone (FSH) begins to increase, stimulating the growth of follicles in the ovaries. As new follicles develop, they secrete oestrogen, a hormone which is important for healthy uterine lining, cervical opening and cervical mucus.
Once a dominant follicle reaches maturation, it produces even higher levels of oestrogen, which in turn causes a temporary surge in luteinising hormone (LH) and FSH, triggering ovulation (the release of the egg) and the formation of the corpus luteum. The corpus luteum then starts to pump out progesterone, preparing the body for pregnancy.
As progesterone levels increase, the BBT will also steadily rise. If the egg has been fertilised during ovulation, then the BBT will remain higher past 16 consecutive days indicating the likelihood of successful fertilisation and conception. If pregnancy does not occur, the BBT will drop, causing a subsequent drop in progesterone, and signalling the onset of a new cycle (day 1 of the bleed) [2].
Why is this relevant to fertility?
Specifically, tracking the BBT over several cycles will show if and when ovulation is occurring and assess the length of the luteal phase, both which are essential to conception and sustaining a healthy pregnancy [3]. Tracking the timing of ovulation is also vital because most women will typically be the most fertile 5 days prior to ovulation and the day of ovulation itself, before they have an increase in their BBT [4]. This is therefore an important consideration for timing of intercourse during the most ‘fertile window’.
But don’t all women ovulate on day 14?
The belief that all women ovulate on day 14 of their cycle is a common myth which needs debunking, as its estimated a mere 10% of women experience a consistent 28 day cycle, resulting in ovulation on day 14. In fact, a normal menstrual cycle is typically between 28-34 days, with ovulation occurring somewhere between days 10-21 [4]. It is important to note that the timing of ovulation can vary from cycle to cycle and from woman to woman. This is why it’s beneficial to track the menstrual cycle using BBT charting for at least three months or more, to gain a better understanding of ovulation patterns. By becoming familiar with the menstrual cycle, one can more accurately estimate when ovulation is likely to occur and therefore the ideal time to conceive.
Symptoms of ovulation
There are some symptoms which may indicate ovulation is occurring, but in clinical experience these symptoms should be noted alongside the BBT for accurate tracking.
Cervical mucus
During the follicular phase, there is an increased level of oestrogen which gives rise to the production of cervical mucus. The cervical mucus itself becomes more abundant and resembles an almost clear, stretchy, and lubricative type mucus, and is often referred as an “egg-white” cervical mucus, indicating that ovulation is occurring or imminent [5].
Increased sexual desire
Higher levels of estrogen can lead to a temporary increase in libido or sexual desire right before ovulation in some women [6].
Mittelschmerz: Mild lower abdominal discomfort
Mittelschmerz – German for “middle pain”, is estimated to affect approximately 40% of women of reproductive age, and is characterised by one-sided, lower abdominal ovulatory pain [7].
Other reasons to chart the BBT
Charting over several cycles also helps us understand if their are any potential underlying hormonal conditions such as hypothyroidism (low thyroid function), endometriosis or polycystic ovarian syndrome (PCOS). A chronically low BBT with fatigue, weight gain, cold sensitivity, irregular menstruation and a slow heart rate may be indicative of an under active thyroid, warranting further investigation. Research has demonstrated a clear correlation between an under active thyroid and impaired ovulation, hence normal thyroid function is necessary for fertility in women, as well as to maintain a healthy pregnancy [8]
An extended follicular phase may be indicative of PCOS if there are additional signs and symptoms, such as abnormal hair growth, insulin resistance (type II diabetes), weight gain, ovarian cysts, fertility concerns, and elevated male androgen hormones (testosterone). In fact, recent studies have revealed that PCOS could be associated with 80% of anovulatory infertility cases [9]. Therefore, extended or abnormal BBT charts with unexplained infertility could be helpful for the potential diagnosis of PCOS.
In the case of endometriosis, a condition where endometrial like-tissue grows outside the uterus, it is very common to see an elevated BBT during menstruation when the BBT would normally drop due to the decrease in progesterone [10]. By charting and understanding these changes in the BBT, women can better track their cycles, help pinpoint ovulation and recognise potential fertility barriers, making it a valuable tool in preconception care.
How to perform a BBT reading correctly
Monitoring BBT from home is actually very simple and straight forward, but there are a couple of key consideration to ensure accurate readings.
- Each morning upon waking, immediately record the BBT using a reliable thermometer, either orally or vaginally. Stick to one method of taking the BBT reading and don’t swap between both routes. It cannot be stressed enough that the BBT must be taken upon waking and not after getting out of bed, as this can skew the readings and give inaccurate charts.
- The BBT should be taken after at least 4 hours of sleep. If you wake during the early morning e.g 4-6am and have had at least 4 hours sleep, then take the temperature at this time. If you’re a shift worker and sleep during the day, then the same rule applies to recording the BBT upon waking, so long as its been at least 4 hours.
- Either write down the BBT reading in a notebook or input the reading in a reliable fertility app. These apps are also useful for inputing other data, such as the duration of menstruation, volume, cervical mucus, and intercourse days.
- Be consistent with taking the BBT every morning to ensure accurate charting across the cycle. Depending on the complexity of the case or when dealing with prolonged infertility, it may be necessary to do this for several cycles whilst undergoing Chinese medicine and/or IVF treatment.
Factors affecting BBT readings
It has been stated twice already, but third times a charm! The BBT must be taken first thing upon waking and not after getting out of bed. This can alter the BBT reading which is enough to give inaccurate data. It is also important to abstain from alcohol as this will cause spikes in the BBT, which is very clear when you see these spikes on a chart. Severe stress, overwork or intensive exercise can cause small drops in the BBT, so this must be taken into consideration. If there is only one or two drops across the entire cycle, then these are typically ignored.
A note on chinese medicine and BBT tracking
Chinese Medicine offers a holistic approach to understanding the menstrual cycle and fertility, viewing the body as an interconnected system influenced by the balance of Qi, Blood, Yin, and Yang. Although a modern application, tracking the BBT can also be very useful tool for Chinese medicine diagnosis and treatment. By assessing the individual signs and symptoms and combining these with the BBT, specific modifications can be made to acupuncture or herbal medicine protocols.
For example, the follicular phase of the cycle is known as the Yin phase in Chinese medicine. Depending on the presentation, certain Chinese herbal formulas or acupuncture points can be applied to build Qi and blood, which are required for the lead-up towards ovulation. If there is excessive follicle stimulation occurring and impaired ovulation in conditions like PCOS, blood moving and dampness resolving formulas can be applied. Or if there are issues surrounding ovulation and the luteal phase (also known as the Yang phase), then Qi moving or Yang warming herbal medicinals can be considered in the treatment plan.
Closing thoughts
BBT charting is a valuable tool for women seeking to understand their menstrual cycle and fertility. It provides critical insights into ovulation patterns and when combined with the holistic approach of Chinese Medicine, BBT charting offers a comprehensive method to support women’s reproductive health and fertility goals. By integrating both scientific and Chinese medicine models of healthcare, women can achieve a deeper understanding of themselves and make better informed decisions about their body and fertility journey.
References:
[1] Steward, K., & Raja, A. (2023). Physiology, Ovulation And Basal Body Temperature. In StatPearls. StatPearls Publishing.
[2] Thiyagarajan, D. K., Basit, H., & Jeanmonod, R. (2022). Physiology, Menstrual Cycle. In StatPearls. StatPearls Publishing
[3] Yu, J. L., Su, Y. F., Zhang, C., Jin, L., Lin, X. H., Chen, L. T., Huang, H. F., & Wu, Y. T. (2022). Tracking of menstrual cycles and prediction of the fertile window via measurements of basal body temperature and heart rate as well as machine-learning algorithms. Reproductive biology and endocrinology : RB&E, 20(1), 118
[4] Wilcox, A. J., Dunson, D., & Baird, D. D. (2000). The timing of the “fertile window” in the menstrual cycle: day specific estimates from a prospective study. BMJ (Clinical research ed.), 321(7271), 1259–1262
[5] Su, H. W., Yi, Y. C., Wei, T. Y., Chang, T. C., & Cheng, C. M. (2017). Detection of ovulation, a review of currently available methods. Bioengineering & translational medicine, 2(3), 238–246
[6] Caruso, S., Agnello, C., Malandrino, C., Lo Presti, L., Cicero, C., & Cianci, S. (2014). Do hormones influence women’s sex? Sexual activity over the menstrual cycle. The journal of sexual medicine, 11(1), 211–221
[7] Brott, N. R., & Le, J. K. (2023). Mittelschmerz. In StatPearls. StatPearls Publishing.
[8] Koyyada, A., & Orsu, P. (2020). Role of hypothyroidism and associated pathways in pregnancy and infertility: Clinical insights. Tzu chi medical journal, 32(4), 312–317
[9] Rababa’h, A. M., Matani, B. R., & Yehya, A. (2022). An update of polycystic ovary syndrome: causes and therapeutics options. Heliyon, 8(10), e11010
[10] Chai, S., & Wild, R. A. (1990). Basal body temperature and endometriosis. Fertility and sterility, 54(6), 1028–1031
