In 1983, John McCarthy and Howard Rockette wrote an academic paper about various basal body temperature monitoring methods. This paper, called a “A comparison of methods to interpret the basal body temperature graph” for all you readers out there, analyzed over 5,000 BBT charts using various charting methods. Before we go any further, I’ll quickly outline the methods they tracked:
In their words: “This procedure uses the highest of the normal temperatures in the low phase as the reference point. The thermal shift is determined once three consecutive temperatures area specified number of degrees above this point.”
In our words: Isolate the highest temperature out of the normal temps in the first half of the biphasic curve. Use this high point as a baseline. When three consecutive temperatures are on or above the baseline, or coverline, the first of those three points is your ovulation date.
In their words: “…The thermal shift can be identified where the BBT curve transects the mean of all temperatures on the graph. This procedure can only beused retrospectively and requires relatively complete charts if it is to be properly utilized.”
In our words: After you’ve temped for an entire month, take the average of all temperature points. When the biphasic curve crosses over the average temperature point, that’s your ovulation date. This method can only be completed after the full cycle is complete.
In their words: “This “smoothed” curve is obtained by replacing the temperature at the ith point, with the average of the three temperatures at the points i – 1, i, and i + 1. The thermal shift is located where the “smoothed” curve transects the average of all temperatures, and all points on the curve remain above this average.”
In our words: SMC is essentially an updated version of the averaging method, that allows for prospective charting as opposed to retrospective.
If you’re thinking WOW, this is confusing, you are not alone! Even the six trained physicians who studied gynecology and/or reproductive endocrinology interpreted BBT graphs differently. Some methods are easier to follow, but tell you ovulation date after it happens. Other methods are harder to use and take multiple cycles to get accurate data, but can usually predict ovulation beforehand (but not always).
It’s also important to add that this study didn’t even TRY to interpret some BBT charts. Which ones you ask? BBT charts for women with irregular cycles. So not only is BBT charting frustrating for women with normal cycles, it’s next to impossible if you have irregular cycles.
Luckily, the iFertracker’s advanced algorithm is designed to create easy-to-read, accurate charts for women with both regular and irregular cycles. Not only that, but the prediction feature can pinpoint ovulation day before it happens never letting you miss your fertile window or day of ovulation. There’s no need to interpret your chart using one of these old-school, confusing methods. We’ll let you know when it’s the best time to TTC!