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Basal Body Temperature: Learn to Measure BBT to Detect Ovulation

Measuring BBT and tracking ovulation with a basal body temperature chart can be tricky at times. Let’s take a quick look at how to do it right and get pregnant quicker.
Measuring BBT

What is basal body temperature?

The basal body temperature (BBT) graph shows that you have ovulated, not that you are about to.

To time intercourse, you should log and monitor your BBT for a minimum of one cycle, better yet two, or even three.

You will see when ovulation has occurred and will be able to plan intercourse for the days leading up to the next temperature rise.

How does BBT сhart change after ovulation?

When an egg is released, the body starts producing progesterone, which raises your body temperature.

Thus, your basal body temperature (BBT) increases after you ovulate, and tracking this can be one way of verifying ovulation.

If you log your temperature each day, you should see an increase at least by 0.72 °F (0.4 °C) the day after you ovulate.

Want to chart your BBT? Flo will help!

Log your BBT every day in Flo, and you will notice the monthly changes in temperature.

BBT in the morning

How do you track ovulation using BBT spikes?

If it is not possible to monitor ovulation by gynecologic ultrasound, there is a way to do it independently by measuring basal body temperature (BBT) every morning and without getting out of bed.

In the first phase of the cycle, BBT usually stays below 98.6 °F (37 °C). Most often BBT falls between 97.52–98.24 °F (36.4–36.8 °C) because of low progesterone concentration.

One day before ovulation, a luteinizing hormone peak is observed, which can be accompanied by an additional decrease in temperature by 0.36–0.54 °F (0.2–0.3 °C.)

After ovulation, the progesterone level sees a sharp increase (approximately 10-fold), which causes a temperature leap above 98.6 °F (37 °C.)

With an adequate corpus luteum function, it will stay at this level for 10–14 days.

If the fertilized egg doesn’t implant, the progesterone level and basal body temperature will decrease before menstruation.

To control ovulation, measure BBT daily for several cycles with no breaks.

Why should you measure basal rather than normal body temperature to track ovulation?

Monitoring your basal body temperature (BBT) is the easiest, cheapest, and the most affordable way to detect ovulation.

The BBT is a “base” temperature normally measured in the morning after having at least 3–4 hours of sleep (rest) before any physical activity.

A body temperature not influenced by any external factors can be considered the most accurate and reliable.

Throughout the day, it fluctuates due to stress, cold, heat, exercise, food intake, etc. Under such conditions, it is impossible to capture a temperature unaffected by the extraneous factors.

When should you chart your BBT?

To monitor ovulation on your own, you can measure your basal body temperature (BBT) daily in the morning before getting out of bed.

Chart your BBT if you:

  • want to monitor and understand the processes taking place in your body
  • want to determine your most fertile days
  • want to predict menstruation
  • suspect hormonal imbalance and reproductive system failures

The BBT chart may warn you about the “unsafe” days during which you should refrain from unprotected sex to avoid unwanted pregnancy (provided your cycle is stable, periods are regular, and the measurements are accurate). However, this is not the most effective method because it depends on many factors (stress, illness, poor sleep, measurement accuracy, etc.) You shouldn’t rely on this method alone.

 

Measuring BBT orally

How to track BBT

  1. Take your temperature every morning at the same time.
  2. Don’t get out of bed and talk (i.e., perform any actions) before taking your temperature.
  3. Always measure the temperature in the same way (orally, vaginally, or rectally).
  4. Use the same thermometer (electronic or other).
  5. You should have had at least 3 hours of sleep before taking the temperature.
  6. Log the measurements in Flo (Android, iOS). 

It is best that you take the measurements for at least three cycles.

The data collected during this time will help determine ovulation and reveal hormonal disorders (if any).

Temperature fluctuations on a BBT Chart

BBT measurements obtained throughout the cycle are entered into a chart that is divided into two phases.

The vertical dividing line corresponds to ovulation. The first phase of the cycle is the chart section that comes before it and the second phase is the one after.

BBT measurement is used to evaluate the ovarian function.

Temperature changes throughout the menstrual cycle are determined by the progesterone’s influence on the thermoregulatory center as well as the fluctuations in the estrogen level.

The temperature during the first phase is predominantly influenced by estrogen, which is the low-temperature phase.
The temperature during the second phase (the high-temperature phase) is controlled by progesterone. Normally, it is higher than that in the first phase.

In the absence of pregnancy, BBT usually decreases approximately 1–2 days before menstruation starts.
This parameter differs on a case-by-case basis. The values ​​can also vary slightly from cycle to cycle.

How accurate is BBT-based ovulation tracking?

According to statistics, in the first year of taking the measurements, this birth control method is 99% effective, if the menstrual cycle is regular.

During this period, women are more responsible and committed. Then, according to research, measuring the temperature regularly becomes a burden, and the method’s effectiveness goes down to 85%.

BBT charting shouldn’t be used as the only contraception method.

What basal body thermometer should you use?

To measure your basal body temperature (BBT), you can use either an electronic or a mercury thermometer.

The one you choose is up to you. The main thing is to use it throughout the entire measurement period.

The electronic thermometer has some advantages over the mercury one. It is safer to use, it signals when the peak temperature is reached, and its memory stores the measurement value (in case you forgot to write it down immediately).

The electronic thermometer is easy to use, while the mercury one has to be shaken down. It is best that you do this before bedtime so that the hand movements don’t affect body temperature measured in the morning.

If the measurement taken with the mercury thermometer ends up in between two markings, opt for the lower one.

What is the most accurate way to measure BBT?

Basal body temperature (BBT) can be measured in three ways: orally, vaginally or rectally. You should adhere to one of them throughout the entire measurement period.

The rectal method is considered the most accurate.

When measuring the temperature orally, the thermometer should be placed under the tongue. The temperature should be measured with your mouth closed for at least 5 minutes (if the mercury thermometer is used) or until you hear a sound signal (when using the electronic one).

As for the vaginal or rectal methods, the waiting period for the mercury thermometer is reduced to 3 minutes.

You shouldn’t measure the BBT using the armpit method because it won’t be accurate.

How to measure BBT if you were active at night

If for some reason, you had to get out of bed at night or you were suffering from insomnia, you should measure your basal body temperature (BBT) after having at least 3–4 hours of continuous sleep.

Otherwise, the results will be inaccurate and will have to be ignored.

If you work at night, you should measure your BBT in the daytime after having had at least 3–4 hours of sleep.

Pregnancy BBT chart

How to detect pregnancy on a BBT chart

If your basal body temperature stays elevated for more than 14 days after a leap indicating ovulation and your period doesn’t arrive, this may indicate pregnancy.

If conception takes place (approximately on day 4–10 after ovulation), the fertilized egg implants itself into the endometrium.
This may be indicated by a sharp temperature drop on your chart, which is due to the fact that pregnancy onset is associated with estrogen release, which lowers the BBT.

The onset of pregnancy sometimes manifests itself through a triphasic pattern on your chart, i.e., there is a third temperature level shown.

This situation is the result of additional progesterone produced by a pregnant woman’s body.

You shouldn’t rely on these signs completely. Sometimes, they can be wrong. To be on the safe side, take a home pregnancy test.

Flo users share their stories: getting pregnant by charting BBT

My husband and I stopped using birth control for a few months, but we weren't trying very actively. I came across FAM (Fertility Awareness Method) and started charting. I have had two infections of the ovaries in the past connected to my celiac, and I was scared that I might not be able to get pregnant at all. After 1 month of temp charting, I was pregnant! Didn't even have to take a pregnancy test because the chart showed so clearly that I had to be pregnant. But still tested a week ago! 5 weeks at this moment!

The perfect BBT chart: what does it look like?

The menstrual cycle consists of two phases (one taking place before ovulation and the other after), which is why the normal basal body temperature (BBT) chart is biphasic, looking like a bird flying upwards.

It shows the temperature drops before ovulation and before menstruation (if pregnancy hasn’t occurred).
Right after ovulation, the BBT rises and stays at that level until the premenstrual drop.

The increase occurring in the second phase should be at least 0.18 °F (0.4 °C) higher compared to the first phase. It is normally observed for about 12–14 days.

When menstruation starts, the BBT usually stands at around 98.6 °F (37 °C) and goes down by the end of your period.

Perfect BBT chart

BBT chart: a monotonous curve

Temperature fluctuations on your BBT chart can help determine ovulation, the onset of the luteal phase, etc.

If the chart shows a steady pattern with no distinct temperature decrease or increase throughout the cycle, this may indicate the absence of ovulation.

Don’t panic. This situation may sometimes be caused by a faulty thermometer.

Try using another one. If there are still no changes, be sure to see a doctor.

Bear in mind that a woman can experience several anovulatory cycles per year, which is normal.

If the situation occurs during every cycle, you should undergo a checkup. The chart alone can’t be used to make a diagnosis.

BBT chart: a zigzag curve

In the absence of pregnancy, your BBT chart should display two temperature levels: a low one observed in the first phase, and a high one in the second.

If there is a zigzag chart with the low and high temperatures constantly alternating, this may indicate estrogen deficiency (provided that the thermometer is fault-free and all measurement instructions were followed correctly).

Try changing your diet and paying more attention to your physical and mental states, and then monitor your chart for three more cycles.

If no changes occur, you should see a gynecologist and undergo an additional examination. The chart alone can’t be used to make a diagnosis.

BBT chart: an erratic curve

If a chaotic curve is observed on your BBT chart for several cycles and there are dramatic temperature leaps (it increases and then goes down with a difference exceeding 1 degree), this may indicate an estrogen deficiency.

This situation can also be the result of random factors, such as a faulty thermometer (in this case, you should replace it and monitor the readings of a new one), non-compliance with temperature measurement rules (i.e., the temperature is taken at different times or using different methods each time), as well as changes in your mental and physical states (stress, fatigue, common cold, etc.).

To dispel doubts, you should see a gynecologist and undergo an additional examination.

When is BBT chart inaccurate?

BBT may not be accurate:

  • if measured at different times and in different ways
  • in the case of a fever
  • when taking certain medications
  • in the event of alcohol consumption the day before
  • in case of emotional or physical stress
  • in the event of a circadian rhythm disorder caused by jet lag
  • when using electric blankets, electric sheets, or heating pads
  • in the event of breastfeeding or insomnia

Charting your BBT would also be futile when taking hormonal contraceptives because in this case, the body is influenced by synthetic hormones that change the menstrual cycle and the ovulation process.

https://www.babymed.com/fertility-awareness/pregnancy-diagnosis-and-bbt-temperature-curve
https://www.verywell.com/body-basal-temperature-chart-to-detect-early-pregnancy-1960284
http://www.who.int/mediacentre/factsheets/fs351/en/
http://www.mayoclinic.org/tests-procedures/basal-body-temperature/basics/how-you-prepare/prc-20019978
http://answers.webmd.com/answers/1189632/how-can-i-tell-when-i

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