Know Your Fertility

Get pregnant naturally. Avoid pregnancy naturally.

Basal Body Temperature and Fertility

on August 19, 2012

TemperatureThe body’s resting temperature increases four-tenths of a degree Fahrenheit or two-tenths of a degree Centigrade under the influence of progesterone at ovulation.

Observing this sign involves taking your temperature at the same time each morning before rising. (This is not as hard as it sounds. It takes less than two minutes and you can go back to sleep if you want.)

To observe your temperature rise, buy a BD brand digital basal thermometer. This brand will give you a consistent and accurate reading. Other high quality brands of digital basal thermometers are also probably accurate, but have not been tested for fertility awareness. Make sure the battery is good. (You can replace it.) An ordinary clinical thermometer is not accurate enough for fertility awareness. Nor is the “ear thermometer” (tympanic thermometer).

Take your temperature every day immediately upon waking, before 7:30 a.m. The body’s rhythms (circadian rhythms) fluctuate over a 24-hour period. Your temperature is lowest in the early morning and highest in the afternoon.Fluctuations are greater after 7:30 a.m. If you go to bed before midnight and wake up before 7:30 a.m., you will get the clearest temperature readings. If it is not convenient to take your temperature immediately upon waking, you may take it during light morning activity. For example, if you need to go to the bathroom, you may take your temperature while getting up and using the toilet. If you are consistently wakened by your baby, you may take your temperature while caring for your baby. But be consistent about the circumstances under which you take your temperature. If you take it during light morning activity, take it that way every morning. Don’t take it sometimes before getting up and at other times during light morning activity. If you have sexual relations, take your temperature before.

Many women find that the digital thermometers require such a short time to use that it is easy to take their temperature before getting up. Take your temperature by mouth. Under arm and ear temperatures are not accurate enough for family planning purposes. The thermometer will beep softly several times before beginning to beep slightly louder and repeatedly. Keep the thermometer under your tongue until the louder, repeated beeps begin.

You can read and chart your temperature as soon as is convenient after taking it.Your thermometer has a recall button that allows you to read the last temperature taken. Be sure to wash your thermometer after each use.

Charting Your Temperature

Put a dot on a graph on the spot corresponding to each day’s temperature. Join the dots of consecutive days. If you do not take your temperature one day, do not join the dots across that day. Also note the temperature numerically.

Interpreting Your Chart

1) Breathe and relax. Study your chart.

2) Can you find six low temperatures on or before Key Day? (If you do not know how to determine key day, you will have to read the article entitled Charting the Fertile Mucus to Avoid Pregnancy.)

3) Draw a horizontal line at the highest of the six low temperatures. This is your low temperature line. (See sample chart.)

4) Draw another horizontal line four-tenths of a degree F. or two-tenths of a degree C. above your low temperature line. This is your full thermal shift line.

5) Can you find three high temperatures after Key Day? All of the high temperatures must be above the low temperature line. At least the third high temperature must be at or above the full thermal shift line.

6) All the low temperatures must be on or before Key Day and all the high temperatures must be after Key Day. This temperature pattern of low and high temperatures is called a biphasic pattern with a full thermal shift.

A biphasic pattern with a full thermal shift confirms that you really did ovulate. If you are avoiding pregnancy, you may consider the ovum dead and yourself infertile the evening (after 6:00 p.m.) of the 4th high temperature day after Key Day. If you are achieving pregnancy, you can feel confident that you really are ovulating.

If your temperature does not rise four-tenths of a degree F. or two-tenths of a degree C. (or at least a smaller, but visible, rise) and stay there until the end of your cycle, it is called a monophasic pattern. A monophasic pattern indicates that you may not have ovulated. (Then again, you can’t be sure.)

A drop in temperature 10 – 15 days after a thermal shift indicates that menstruation is about to begin that day or within 48 hours. Probably that day. If your temperature stays high for 18 days or so after the high temperature begins, you are most likely pregnant. Congratulations.

For more information, and a sample chart for the basal body temperature, see the free download, Fertility Awareness, at www.knowyourfertility,net.

– Marie

6 Responses to “Basal Body Temperature and Fertility”

  1. I hope your life more wonderful’s a I’m very glad to see such magnificent information being shared freely out there. post.

    • Raj says:

      I used it, but honestly gave up brefoe getting pregnant because I didn’t find it added value beyond using OPK sticks, it just was a much bigger price tag. it didn’t give me any new information and I always got my peak reading the day after getting an OPK+, which made me wonder if I would have missed part of the window if I had relied on the monitor only. (yes, I was obsessing enough to try both at once!) I also think in the case where you are having ovulatory issues (I am in the camp too), you don’t need a $300 monitor to tell you that OPKs will give you the same answer (never positive if there’s no LH surge). but really, charting is best because you can have a surge and still not ovulate. I thought charting with OPKs, if you are willing to put in the effort, was the most informative answer. but I certainly shelled out for that monitor brefoe coming to that conclusion because if there was any chance it would help, I wanted it!

      • marie says:

        One of the reasons women like natural fertility awareness is because it is free. One of the problems with the OPK sticks is that they measure what is in the urine. Remember that, once it is in the urine, it has been in the blood for at least a day or two. This means that fertility begins before the OPK stick show it. If you are avoiding pregnancy, that is bad news. But if you are achieving pregnancy, you are fine. Only that, as you say, you had to buy something to know your body. Most women in the world do not have the luxury of buying the OPK sticks from the drug store. I always feel that knowledge is power.

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    • Enrique says:

      i sorta agree with kkuether. i used the OPKs (evenings) with the FM stkics (mornings) and the OPKs did pick it up earlier, but i think it’s because i did it at night. i think you typically surge in the evenings (at least that’s the case with me). the good thing about the FM is that it gives you high fertility days. because there is a RANGE of days that you are fertile because the sperm lasts for a few days. OPKs do not. OPKs just give you that 1 day of surge.

      • Jeremy says:

        I tried OPK tests and ended up spending more due to hanvig irregular periods. I also was never consistent with charting my BBT and found the monitor although expensive more convenient. Over time, I didn’t have to use as many test sticks to determine when I was ovulating. I didn’t get pregnant using it, but at least I was ovulating. I would try anything to have a baby!

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