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Using Your Basal Body Temp to Help Determine your Risk of Pregnancy


Basal Body Temperature (BBT) is your body's resting/waking temperature, normally it is used to chart a woman's fertility patterns. It is used to confirm the passage of ovulation, but will not give any warning of approaching ovulation. It can do this because the hormone progesterone which is released in quantity only after ovulation has occurred will cause the body's internal temperature to rise slightly this confirms the passing of ovulation and fertility for that particular cycle.

This web page will focus on using this method in emergency situations, to try and identify if ovulation has yet occurred. I'm expecting that most of you will not have been charting your BBT before finding this page. That's ok. With the information you will gather by taking your BBT, and with the help of other pages on this website, you will hopefully be able to get a decent idea of where your cycle is at. It might not be able to help in every case, but for some or most women, I think it will help. Either way, it provides another tool to help you determine what your body is doing.

First thing you will need will be a digital thermometer, if you happen to have a basal thermometer on hand that's fine, it will work too. A regular fever thermometer will not work, it MUST be able to measure a 10th of a degree, only digital or basal thermometers do this. Digital thermometers are very common, and can be purchased at any drugstore, Wal-mart, or similar store.

When concerned about getting pregnant, time is of the essence. Every day matters, especially when it comes to your BBT - things can change very quickly, if at all possible, get everything ready so you can take your temp first thing in the morning, as in tomorrow morning. You will need to take your temp before getting out of bed, before drinking any fluids, before putting anything in your mouth, before sex, before anything at all. This is very important, if you get up to go to the bathroom, the movement will cause your body temp to rise and will give an inaccurate and misleading temperature reading, or if you drink something again the temp in your mouth will change and will be inaccurate. It is also important to take your temp at the same time each morning, you will need to do this for several days, to get an accurate idea, one days temperature will not be enough. So set your alarm next to your bed, so you can reach over turn it off, and put the thermometer right in your mouth. When finished, write it down.

Summary -

What you will need:

  • a digital thermometer
  • paper & pen
  • alarm clock

What to do:

  • Place everything in arms reach of your bed, including the alarm clock.
  • set the alarm at the time you will get up each day. Its important to take your temps at the same time each morning.
  • when the alarm goes off, don't sit up to turn it off, don't get out of bed, roll over and turn it off.
  • take your temperature
  • write it down - then you can do whatever you want!

After ovulation occurs a rapid chain of events follow. Once the egg leaves the ovary, luteinizing hormone (which triggered ovulation) transforms the ruptured follicle (that housed the egg during development) into the corpus luteum which begins to secrete progesterone. Progesterone's function is to finish preparing the endometrium incase an egg is fertilized. As progesterone gets into the bloodstream, one of its effects is to cause the body's temperature to rise slightly, usually occurring about two days after ovulation, depending on the individual. This change would not be noticeable with a regular fever thermometer, but with a digital or basal thermometer, the change is noticeable, and even more so when the temps are recorded on a chart.

Using a chart may be helpful, especially if things don't seem to be clear cut. Seeing things visually will really help. The above link has several charts to choose from, any basic chart for BBT will do. Remember that Day 1 was the first day of your last period, so if you have this information it will be really helpful. So mark the date your last period started on Day 1 of your chart, then add your temps in on the appropriate dates, and connect the dots with a line. View some charts online to get a better idea of what a chart should look like.


***Things to keep in mind with the BBT, temps need to be taken at the same time each morning. No warning of approaching ovulation, only confirmation when it has passed. a minimum of 3 hours sleep is needed for an accurate temp. Getting out of bed, any activity, drinking something, even a nightmare can alter your resting temps making them inaccurate or misleading (higher than it would have been), so taking your temps for a minimum of a week is recommended, and longer may be better. There are certain advantages to charting the remainder of your cycle. This method can confirm pregnancy if used for the next 25 days.

This is very basic information, just to help get an idea of where you are in your cycle. BBT can be used daily to chart your fertility. However, read up on it before basing any contraceptive decisions on it (like whether or not to use contraception). A really excellent book on BBT is Taking Charge of your Fertility by Toni Weschler, which I highly recommend. It should be part of every menstruating girl/woman's library. It will thoroughly explain how to read your charts what the different patterns mean and just tons and tons of really great information.


So what does it all mean & How can you use this information?

In an emergency situation chances are you won't have any previously recorded history to look back on to see what is normal for you, so we'll just have to wing it and use generalities.

In general, before ovulation occurs, resting body temps will be in the low 97.0's - probably 97.4 or below, they can also be in the higher 96.0's like around 96.8 degrees. After ovulation, body temps will be in the higher 97.0's - 97.6 or above, they can also be in the 98.0's though usually not higher than 98.3, but again, individuals will vary. So what if your temp is in between, like 97.5? Best you can do is keep charting your temps each morning and see if it moves one way or the other.

Here is a picture of a typical cycle.
what a typical cycle looks like when BBT is charted for the entire cycle.

Chances are you started charting somewhere in the middle of your cycle so you won't have as much information to work with. But see how there is a noticeable temperature rise? The dots that are darkened represent the days leading up to ovulation and ovulation will occur during those days. More Non-Pregnant Charts


Remember you can't tell where you are in your cycle from one or two days of temperature recording. Our bodies occasionally throw in a fluke high or low temperature just to keep things interesting. This method relies on the daily charting so that you can see a pattern develop.



If your BBT is less than 97.4 degrees, then chances are that ovulation has not yet occurred or could be happening at that very moment! Keep recording and look for your temps to rise, remember they won't go up until a couple of days after ovulation has occurred. Ovulation will occur while your temps are still low. If you have had unprotected sex, less than 72 hours ago, you may want to consider going for emergency contraceptive pills, which you can get from Planned Parenthood. Or visit my page on determining your risk of pregnancy, to see if you can figure out how close to ovulation you are. The day ovulation occurs on can vary from cycle to cycle and be influenced by events in our lives such as stress or illness. Predicting when ovulation will occur is difficult, and can only be a educated guess at best. Keep in mind, healthy sperm can survive up to 7 days in fertile conditions.

If your resting body temp is at or above 97.8 degrees, then chances are good that ovulation has already occurred. If it is at or above 98.0 degrees, then ovulation is likely to be past, and the egg may have already expired, and pregnancy would be less likely to occur, and one may even go as far as to say you are out of the woods, but continue to chart for a few more days just to make sure, charting for a week would be even better. Usually, the BBT will rise a couple of days after ovulation has occurred. The egg can be fertilized for 12 hours maybe longer, at least one source says up to 36 hours, but most sources say less than that. Menstruation follows ovulation by 14 days, this is pretty consistent in almost all women. So bleeding should start within 14 days or less.

For women who have long cycles chances are they are not ovulating or it takes estrogen levels a long time to build up enough for ovulation to occur. Typical charts for these women tend to bounce around a lot. If no pattern seems to be developing, and you are prone to long cycles or cycle irregularly you may not be ovulating. This is what an anovulatory chart may look like.
For other examples, visit Anovlatory Charts
example of an anovlatory chart (not ovulating)


This method can also give clues when pregnancy is present. If you choose to chart longer than the initial week discussed here, if conception did occur some women notice a second increase in temperatures about the time implantation occurs, 6 days after ovulation. When this happens it is called a triphasic pattern. This doesn't happen for everyone who conceives but it does happen for some.

Another way the BBT method can identify pregnancy is the length of time that the temperatures stay high. The luteal (post-ovulation) phase last about 14 days for most women. If your BBT is above 98.0 degrees for more than 16 days in a row, then chances are good that pregnancy is present, and more than 18 days a pregnancy test is pretty much guaranteed to be positive. The earliest pregnancy tests can be used 10 days after ovulation.
Ovusoft also has triphasic charts in their gallery.

This image is a typical pregnancy pattern. It has a barely discernible second rise the day after implantation occurred, from there temps continue to stay between 98.1 and 98.5 degrees. Plus temps stay high for more than 18 days a sure sign of pregnancy.
typical bbt pregnant pattern

If a triphasic pattern begins to develop (temps stay elevated for 3 days or more) any herbal abortive used 5 to 7 days before menses is due may cause the pregnancy to abort. An indication of this happening or about to happen, temps will start to fall, as shown in this chart.

If you would like to see examples of other women's charting with BBT, visit Ovusoft.com. Ovusoft started out as Lifecycle.com and they offered free software for you to record your temps in and some notes, they also had a feature that allowed you to upload your BBT charts online, which made it really handy for getting help in enterperting them. A number of years back Lifecycle hooked up with Toni Weschler, and they became Ovusoft.com, they revamped the software and started charging $40 for it. They still offer the website, and uploading for your charts.


This site Copyright 1998 - 2010 by Sister Zeus

This page was created March 5, 2001 and last edited June 20, 2001
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