Take your basal body temperature on waking, before any activity, at the same time every day, with a digital thermometer accurate to 0.01°C, always by the same route, and chart it daily. The change you are trying to catch is only a few tenths of a degree, so small slips in method can hide it.
Basal body temperature is the second most used sign among TTC women. Its value depends entirely on method, because the signal it gives is small.
It is your temperature at rest, taken on waking and before any activity. Before ovulation it sits between 36.2°C and 36.5°C. After ovulation, progesterone produced by the corpus luteum raises it by 0.3°C to 0.5°C and holds it between 36.6°C and 37.1°C until the end of the cycle.
That small rise is the whole signal. A 30-minute shift in timing alone can move the reading by 0.1°C to 0.2°C, which is why the method is strict about routine.
Vaginal and rectal readings are more precise than oral, but the key is not to switch: compare readings taken the same way, every day of the cycle.
In the book's complete system, the daily routine takes 2 minutes a day: in the morning, take your basal temperature before getting up and write it down; through the day, check cervical mucus every time you use the bathroom; at night, log the day's mucus, temperature and symptoms.
Before trusting a reading, consider whether any of the following happened:
| Factor | Likely impact |
|---|---|
| Poor night's sleep (under 5 hours) | Unreliable reading |
| Alcohol the night before | Elevated temperature |
| Cold or fever | Artificially high temperature |
| Shift in timing (over 30 minutes) | Variation of 0.1°C to 0.2°C |
| Night shifts or irregular sleep cycle | Makes the method unworkable |
| Sex before measuring | Can raise the reading |
Basal body temperature is Chapter 16 of Map to the Positive, in Station II (Attunement). After the method, the chapter shows how to read the chart, explains the method's one big limitation, and gives you the combination with cervical mucus that marks both the beginning and the end of your fertile window. Station II closes by bringing every sign together into your personal map.
Take 30 days. If it does not give you more clarity than everything you have read for free so far, ask for a refund and you get every cent back. We cannot promise you a pregnancy. We can promise you will not be guessing.