Basal Body Temperature is used to find out when ovulation will occur. For most women, it is basically standard – low means 97.0 F range. High means 98.0 range, with a .4 rise the day after ovulation and a 14 day luteal phase. The luteal phase means the time from ovulation to menstruation or the start of the next cycle. However, for some women there are some variations on their temperature charts. But there are several possible explanations for these variations.
High temperatures on the whole chart
Consistently high temperatures on the whole chart (especially in the first half of the cycle) may be a sign of a "hyper" thyroid. You must see your doctor and have a thyroid test. Either this will rule out the possibility of a thyroid dysfunction or confirm that your thyroid is indeed hyper-active. If you do have a hyper-active thyroid, your doctor will prescribe medications that will help balance the thyroid. These medications should also help your temperatures go back to normal.
Low temperatures on the whole chart
On the other hand, consistently low temperatures on the entire chart (in both halves of the cycle) may be a sign of a "hypo" thyroid or a low thyroid. You should also see your doctor for tests and treatment of a hypo-thyroid.
Both hypo and hyper thyroid can cause infertility.
Apart from a dysfunctional thyroid, hormonal imbalances may also cause very low or very high temperatures. For instance, low estrogen may cause pre-ovulatory temperatures to be higher than normal, while high estrogen may cause temperatures to be lower than usual. And as with other reproductive hormones, imbalances in any of them will cause variations in your temperatures.
Slow Upward Shift
A woman with a fairly normal chart but then slowly rises upward after ovulation may cause difficulty in determining the exact date of ovulation. There is usually a .4 of a degree shift in temperature when ovulation occurs. However, if the shift happens on one-tenth increments, it will be more difficult to point the exact date of ovulation. For increased accuracy, be extra attentive to the other signs of ovulation such as cervical fluid and/or cervical positions.
No Shift, Erratic Temperatures
There are instances when a woman has erratic temperatures. These cases where her temperature is all over the place from the start until the end of the cycle is known as anovulation. Anovulation is the absence of ovulation. Anovulation can happen even with menstrual bleeding each month. This is common in women who take birth control pills. They do not ovulate yet then bleed during "period" time. The chart will look like any of the following: all low temperatures, all high temperatures or erratic temperatures.
To know more about basal body temperatures, consult you doctor and/or bring your chart for clarifications.