A basal body temperature (BBT) is the lowest temperature of the body during the period of day that is usually attained during rest, which, for most women, is after three or more hours of uninterrupted sleep. In women, the BBT is also affected by hormones, most notably estrogen and progesterone. Before ovulation when the body is dominated by estrogen, the basal body temperature remains low. However, after ovulation, when progesterone dominates, the BBT increases on average around half a degree.
In many women, a noticeable temperature spike occurs immediately after ovulation due to the increase in progesterone and decrease in estrogen. However, not all women who ovulate experience an ideal thermal shift. The following sections describe some of the non-ideal but perfectly normal basal body temperature chart patterns.
Basal Body Temperature Patterns
The first variation in the basal body temperature chart pattern is the sloping rise. In a sloping rise pattern, a thermal shift is obvious, but the individual temperatures rise more gently in a curved pattern over a few days rather than abruptly. Eventually, the post-ovulation temperatures plateau at least half of a degree above the pre-ovulation temperatures.
The second variation in the BBT chart pattern is the slow rise, which is extremely similar to the sloping rise. In a slow rise pattern, a thermal shift is not necessarily obvious until a few days after ovulation. Like the sloping rise, temperatures in a slow rise increase gradually but in even smaller increments and over a longer period of time. The temperatures, too, eventually reach the highest post-ovulation temperatures after four to six days.
The third variation in the basal body temperature chart pattern is the fallback rise or fallback thermal shift. In a fallback rise, an obvious thermal shift occurs immediately after ovulation. But the next day the temperature drops, sometimes under the coverline. However, on the third day after ovulation, the temperatures return to high post-ovulation temperatures and continue to remain high.
The fourth variation in the BBT chart pattern is the staircase rise. In a staircase rise, a thermal shift is not always obvious. Temperatures generally alternatively increase and decrease over a period of a few days until reaching the highest post-ovulation elevated temperatures. Sometimes, the first decrease falls below the coverline.
Other Irregular Temperatures
In addition to the four variations in the basal body temperature chart, other irregular temperatures sometimes happen and make reading the BBT chart more difficult. The first irregular temperature is a significant temperature drop immediately before the thermal shift. Such a decrease is often referred to as an ovulation dip and is the result of an increase in estrogen immediately before ovulation. Not all women experience an ovulation dip.
The second irregular temperature is a significant temperature drop about a week after ovulation. Such a decrease is often referred to as an implantation dip and is the result of a fertilized egg burrowing into the uterine wall. An implantation dip may be accompanied by implantation bleeding. Not all women who have conceived experience an implantation dip, nor does a dip after ovulation always indicate pregnancy.
The third irregular temperature is a temperature that seems out of place either before ovulation or during the luteal phase after ovulation. In general, out-of-place temperatures may be explained by an insufficient period of rest before the taking of the basal body temperature. By following the rule of thumb, a woman may ignore one or two unusual temperatures before or after ovulation when reading her chart.
Although some women experience a clear shift in their basal body temperature immediately following ovulation, not all women can identify such obvious patterns in their BBT charts. Fortunately, some variation and irregularity is perfect normal. Ovulation is possible without an obvious temperature shift as clearly demonstrated by the four variations in basal body temperature.
Sources
Taking Charge of Your Fertility: The Definitive Guide to Natural Birth Control, Pregnancy Achievement, and Reproductive Health by Toni Weschler
Disclaimer: The information contained in this article is for educational purposes only and should not be used for diagnosis or to guide treatment without the opinion of a health professional. Any reader who is concerned about his or her health should contact a doctor for advice.
Heather Marie Kosur - About Me I earned a BA in English studies with a minor in creative writing from Illinois State University in May 2007 and an MS in ...
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