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Reading Your BBT Chart

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Your BBT Chart and Getting Pregnant: What Can BBT Charting Tell me about Ovulation, Implantation, and Pregnancy?

When women start BBT charting, the first and primary objective is to learn about one's unique menstrual cycle and determine when you are fertile. To this end, the BBT chart is instrumental in telling you when you ovulate each month - and based on graphing your monthly "basal temperature spike", you can determine your ovulation date and anticipate those days of the month you will most likely get pregnant.

However, women who have been BBT charting for a number of months or have experience from previous pregnancies quickly extrapolate other applications from their BBT data. And other questions often arise:

  • Can my BBT Chart diagnose infertility issues or hormonal imbalances?
  • Is it possible to diagnose a pregnancy with a BBT chart?
  • Can my chart pinpoint an implantation date?

To learn the how-to of BBT charting, visit our BBT charting guidelines

These are advanced and somewhat controversial applications, and because human fertility is so complex, some women may be able to use their charts to answer the above questions, while other women will not be able to decode their charts without a great deal of ambiguity at all. In effect, while your chart my provide clear data about when you ovulate, in many cases other applications often enter the realm of pure speculation... Before we delve into these issues above, let's do a quick review of BBT charting and human fertility and see how your fertility chart "mirrors" changes in your body and reflects fluctuation in key reproductive hormones.

Reviewing the Fundamentals: Basal Body Temperature and Progesterone

Estrogen is reproductive hormone that crests during the first part of your cycle. In configurative terms for our purposes here, estrogen is the "nurturing" agent, the hormone that prepares the womb for a pregnancy, that cultivates blood flow to the uterus, that swells the uterine lining with blood vessels and tissues, and that helps the reproductive organs produce cervical mucus and soften the cervix. For approximately one-half of your cycle, your body prepares itself for ovulation and pregnancy.

During the "other" half of your menstrual cycle, a new hormone ascends to prominence, taking over as the estrogens recede (approximately twenty-four hours after you ovulate). Of course, this hormone is progesterone. It's function is to provide warmth and in the case of a pregnancy, to prevent menstruation. A BBT Chart is biphasic: it provides a clear graphical image of when ovulation occurs, marked by a sharp rise in body temperature. This basal temperature rise will vary among women, depending on several impacting fertility factors, but will typically conform to a 0.4 to 1.0 F thermal "spike". Please take a look at the image below. Right about midcycle, you'll see the dramatic basal temperature shift - and this indicates that ovulation has taken place. (Note that BBT charting does not "predict" when you ovulate within a discrete cycle; it only verifies ovulation approximately 24 to 48 hours afterwards. Hence, charting your BBTs for just one month provides useful fertility information. However, only after a handful of months will your BBT and fertility data begin to become crystal clear and determinate patterns begin to emerge).

BBT Temperature Chart

Let's return to the image to the left: In a biphasic BBT chart, you'll see your menstrual cycle divided into its two phases - the cool and the hot - with each phase reflecting the dominance of either estrogen or progesterone (and with your ovulation day marking the middle-point separating these phases). During the second half of your cycle, note that your BBT temperature remains high. This is because progesterone is produced until one of two things happens. In the case of a pregnancy, the fertilized egg will implant in the uterus about a week after you ovulate. Following implantation, the embryo will release another hormone, hCG, into the mother's system, and this hormone will tell the body to keep the progesterone high. This, in turn, effectuates amenorrhea - or the interruption of the menstrual cycle. If progesterone keeps cresting, you'll see your BBT temperature remain high and you should experience one of your first pregnancy symptoms: A missed period.

On the other hand, if you are not pregnant, the message to keep progesterone flowing will not be broadcast through your body, and therefore progesterone levels will drop (along with your basal body temperature). And when you see this thermal decrease in your basal temperature, it's likely that menstruation will soon ensue and your cycle will begin anew. The image above displays the red line's fall, paralleling the culmination of a particular menstrual cycle and the onset of menses (your period).

What We Learn from Our BBT Chart: As you can see, we can learn much from our chart, particularly about ovulation and general cycle trends.

We can learn the average length of our menstrual cycle. We can discover if our cycles are regular or irregular. We'll get a graphical display of when we ovulate each month (allowing us to time intercourse at maximum fertility). We can determine the relative length of our two cycle phases. If our BBT temperature does not drop (or stays high longer than previous cycles) we may discover one of our first early pregnancy signs. If our cycles are irregular, quite long or very short, we can also get an inkling that there may be issues to discuss with a doctor.

In a situation when the second half of our cycle following ovulation is very short, this may be an indication of insufficient progesterone levels (or luteal phase defect). In short, luteal phase defect is characterized by the failure of the corpus luteum to generate enough progesterone to keep a discrete cycle going. A luteal phase defect can only be diagnosed by a doctor - and a BBT chart can only alert us to possible fertility issues (it should not be used for "home" diagnoses or guesswork). Luteal phase defects are not uncommon and your doctor can likely provide treatment. If your BBT chart shows inconsistency or displays unexpected temperature shifts (or no temperature spike at all) then share your charting records with your doctor. Here, selecting a proper basal thermometer and simply charting correctly (observing all the very specific guidelines) may prevent any frustration with inconsistent results.

Next Question: Can my BBT Chart diagnose a pregnancy? While a BBT chart cannot give you an unequivocal diagnosis, it can provide a compelling indication that you might indeed be pregnant (or that you should take a pregnancy test). If your BBT temperature stays high longer than usual (based on previous records), it could be a a sign of pregnancy.

The triphasic curve and implantation: Some women who have been charting for a while and have an intimate familiarity with their own BBT histories and patterns may look for a slight decrease in BBT temperature during the luteal phase, about a week or so after ovulation. This dip would, in theory, be followed a day later by a resumed high temperatures - a third phase of the cycle following a pregnancy. The problem with the "triphasic" curve is that there are simply too many variables for it to be an accurate indicator of implantation or pregnancy. Hence, while a prolonged thermal increase may indicate a pregnancy, its not advocated to look for an implantation dip or triphasic chart.

To learn more about the how-to of BBT and fertility charting, please click here and visit: BBT Charting Instructions

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