Reading Your BBT Chart

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).

Biphasic BBT Chart

Let's return to the image above: 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
Learn more about preconception.
Learn about timing intercourse.



I started using this method one yr after the birth of my dd when the iud I had after her implanted into my uterus. Having it removed went fine but i had a pretty bad run with depression from the hormone withdrawals for i have been on some kind of birth control from age 13( heavy/ irregular cycle) 11 yrs - 9 months

I really wish this was part of sex-ed or at least an option
v card till 21 by choice
Teen mom for a mother who bailed after 14 months
Didn't want to be her

This is not a schools responsibilty to teach, it is a patents. This method does not control diseases and infections. Teens should not be taught this as a reliable form of contraception.

I would agree to all that has been said here. I think that there should be a way to teach young girls how to understand their bodies cycle, fertility, and the importance you should have for charting and reading those charts. This should be taught at school or by the parent/guardian at some time in the young ladies life. At some point when she becomes a women and does make the decision to have a child she will understand the way her body works. Often we don't get all the information that would help us become successful in conception or not to conceive because we were not taught, or do not understand our bodies signs. Let alone able to infer the charts that helps with our fertility cycle.

Hi. I'm 36 y/o and learning to chart after a recent miscarriage and trying to conceive again. I have found that it helps a lot to learn about cervical position and cervical mucous in correlation to BBT charting whether you're using this method for contraceptive or conception.
A lot of people are commenting on not being taught the BBT method of birth control in school. The thing is, teens are rarely responsible enough to take a BC pill at the same time everyday, let alone taking and writing their basal body temperature at the same time each day. Also, many teen girls WANT to become pregnant and might use this method for ttc, rather than the opposite. My teenage daughter is using the Depo shot and condoms for BC. I will not be teaching her this method until she's an adult and ready to conceive or at least responsible enough to use it wisely, either way.

And a good one for the opposite. Simply, the chart lets you know if you've ovulated already, and as sperm can live in the female body up to 72 hours, either u practice abstinence during all the first half of your cycle, or you're way in for a surprise.

I'm 42 and am trying to get pregnant. I didn't learn about charting until I first started trying to get pregnant about 4 years ago and a friend made me a gift of a book that discussed this method. It's great, and there really was no person that ever thought to mention it until my one friend. Not a teacher, not a counselor, not a primary care physician, and most surprising, not an ob-gyn. And very difficult and very sad for me to say given my current circumstances (and several miscarriages), I had an abortion at 19. I wish to goodness someone had told me about this before then.

Im 39 and have 2 teen daughters. I'm just now beginning to learn of this option for birth control. Im absolutely loving it. My body doesnt handle the hormone birth controls at all, copper IUD is out of the question as it causes heavier bleeding and worse cramping and if I bleed any heavier I will likely need a tranfusion each month and my cramps already put me to bed each month. My partner and I love spontaneous sex, so a cap, sponge and diaphragm arent suitable aside from the fact that I will not expose either of is to spermicidal chemicals! and finally, the condoms..... they are ok, honestly we prefer the feel of flesh. I too think its important to teach our children about this, and all things about the human bodies. As Always, the more natural something is, the safer we are. One thing to keep in mind that does concern me is that if/when we teach teens about this, we must absolutely continue to push male/female condoms as this, aside from abstinence is the only protection they have against STD's. Teaching a girl to be aware of her cycle is great, so long as she doesnt think as the "safe" days as days thats its OK to have "unprotected sex". Pregnancy is only one of MANY things she needs to protect her body from.

I am a pharmacist and I was not taught about this in college. After around 18 years of practice in profession, I accidentally read this article and understood the concept. However, more information may be accumulated on this subject to study the effectiveness of Emergency contraceptive pills Levonorgestrel Tablets 0.15 mg one tablet regimen.

They most certainly did NOT teach this in any school I went to. Luckily Ive learned some by reading my mothers books and the internet but this should be part of education in school. Im 25 by the way

They most definitely do NOT teach this in school. At least, no school that Ive been to. Ive been lucky enough to learn a little reading my moms books and the internet but NO THANKS to school. Im 25 by the way

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By TTC veteran and mother of two, Elizabeth Andrews.