The Gap Method is a technique that factors in temperature data from both a female and male partner. While the female temperature is expected to vary during her menstrual cycle, the male temperature should not. This technique uses the male temperature as a control group to cancel out environmental influences on recorded temperature.
The Gap Method
Researchers at Emory University School of Medicine in Atlanta, Georgia originally proposed the Gap Method. Hormonal changes during the menstrual cycle cause temperature shifts that are indicative of ovulation. These temperature shifts are well correlated with ovulation. In practice though, it can be difficult to detect the temperature change due to external environmental factors. These cause non-hormonal temperature variations, which can make it harder to interpret a temperature chart and pick out the hormonal shift.
This technique tries to cancel out the environmental temperature variation by using the daily basal body temperature of a male partner as a reference. If both partners are subjected to similar environmental conditions, the external influences on temperature can cancel. This would ideally only leave the hormonal temperature shift and make identification of ovulation much easier.
In order for this approach to work, both partners must share similar environmental conditions. Since temperatures are best taken in the morning, both partners should sleep in the same room. It is also best if they have similar schedules and can wake up to take their temperature at the same time. In the research study, participants took their individual basal body temperatures within 3 minutes of one another.
The relationship between basal body temperatures in females and fertility is well established. As described on this site, progesterone is responsible for a temperature shift around the time of ovulation. The Gap Method of temperature charting takes advantage of this same information, but attempts to improve the integrity of the analyzed temperature data.
- Use a thermometer that is accurate to at least 0.1 degrees.
- Take your temperature immediately after waking each morning before doing anything. Your thermometer should be kept bedside so you can take it without getting out of bed.
- You and your partner should each take your own temperature within about 3 minutes of one another
- Record both temperature values and clearly identify which temperature is which.
- Note any special circumstances that may influence you or your partner's temperature.
Once several temperatures have been recorded, the difference between the temperatures can be charted and analyzed.
- For each day, chart the difference (the 'gap' between the two recorded temperatures
- After the tenth day of your cycle, draw a coverline. The coverline should be 0.20 degrees Fahrenheit above the highest temperature difference seen during the first ten days of your cycle.
- Monitor your temperature chart daily. Look for the temperature gap to exceed your coverline.
- After the temperature stays above the coverline for three consecutive days, you can confirm that ovulation occurred.
- Holds the potential to make temperature charts easier to interpret and analyze by canceling out some environmental effects.
- Quantitative data is easy to record.
- Uses the proven temperature shift caused by progesterone that accompanies ovulation to detect ovulation.
- Can accompany normal basal body temperature interpretation and act as a cross check.
- Requires both partners to regularly take temperatures
- If your partner has temperature variations that are not mutual, it can make your temperature data more difficult to read.
- Like normal basal body temperatures, this technique can only identify ovulation after the fact.
- This is a more modern technique that has not seen years of testing and practice needed to fully understand its effectiveness.
 Dunlop, Allen, & Frank (2000). Involving the Male Partner for Interpreting the Basal Body Temperature Graph. Obstetrics & Gynecology.
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