Basal Body Temperature Basics, Pros & Cons & a brief how-to

If you are trying to conceive a child, knowing when you ovulate is obviously helpful. Not every woman ovulates at the exact same point during her cycle, however, making any sort of standardized assumptions irrelevant. In order to know when you ovulate and when your best chances of conceiving are, you need a reliable fertility measurement system.

Now, it might seem strange the first time you hear of it, but there is a way to track your fertility throughout the month, without even getting out of bed. That method is BBT charting, named for the measurement you track: your basal body temperature (BBT).

What is BBT? The basal body temperature is your temperature immediately after you wake up in the morning, before you do anything. A woman’s basal temperature changes in a regular pattern throughout her cycle, based on hormonal changes in her body. Tracking your temperature is a way of tracking your reproductive hormones, and thereby knowing just where you are in your cycle. That’s it in a nutshell, really. However, the process of charting your BBT involves a bit more information, which we will get to shortly. It is important we look at some of the pros and cons of using BBT as a fertility metric before you decide to plunge right in.

What Are the Benefits of Using BBT?

The benefits of using BBT are numerous for figuring out when you are or will be most fertile. It is inexpensive, with basal thermometers being only a modest, one-time outlay. It is low impact, as the most invasive thing you have to do is put the thermometer in your mouth. It is low-mess—it only involves a small thermometer, some sheets of paper, and a pencil, which you can stow in your bedside table. (And, it gives you excellent justification for lying in bed just that one minute longer!)

But BBT tracking brings with it many other benefits as well, according to Dr. Angie Beltsos, OB/GYN, Medical Director of Fertility Centers of Illinois. BBT is a good way of showing when conception has occurred—your temperature stays elevated when it would otherwise drop. It can also help uncover certain fertility issues such as the luteal phase defect, which is when you appear to have a period between ovulation and menstruation. Its primary benefit for those seeking to conceive, however, is acting as a means of tracking the “consistency of ovulation,” says Beltsos. Once you are familiar with your cycle, you will be much more aware of when is the right time to try. You will also simply know your body better through close observation, and that will help with both trying to conceive and maintaining your health in general.

Should you ever decide to see a fertility specialist, you will have a load of empirical evidence to share with her.

What about the Drawbacks?

While there are no serious drawbacks to using BBT—there aren’t any side effects or anything like that—there are a few reasons why this method may not be right for you. For instance, it takes some patience. What you are really looking for is patterns, which will only emerge after regular tracking for more than a month. You have to be consistent too, taking your temperature every morning.

Basal body temperature can be affected by external factors, such as taking certain medications or your activity level, so if you don’t take note of those factors your results may seem confusing.

“The main downfall with tracking basal body temperature and ovulation is that with this method, you don’t actually know you’re ovulating until the tracked temperature goes up,” says Beltsos, which means that your fertile window has already passed. This can be frustrating until you have charted your temperature for several months and can read and predict the patterns. In other words, you won’t get an indication as to when you would conceive the first month you chart your BBT.

How Successful Is BBT in Predicting Fertility?

“BBT is very good at showing that ovulation has occurred,” says Beltsos. Functional ovulation is, of course, integral to a woman’s ability to conceive, and BBT tracking will let you know whether your symptoms of ovulation are regular or even present. It can reveal other cyclical problems too, but if you have other fertility issues, such as blocked fallopian tubes or endometriosis, tracking your BBT will not necessarily expose them.

Charting Your BBT: A Step-by-Step Guide

In order to begin charting your basal body temperature, you need two things: a good digital BBT thermometer and a place to chart. (Most thermometers come with a chart.) Now, you will want to keep these materials right next to your bed so you can take your temperature immediately after you wake up each morning. “It is important that the temperature is measured while [your] head is still on the pillow,” says Beltsos. Then write down the temperature on the chart.

The basal thermometer is different from the ordinary household thermometer used for detecting fever. It makes smaller changes easier to detect. We’re not talking huge swings of temperature here, but fractions of a degree.

In order for you to really benefit from charting your BBT, you need to know what to expect. Remember: The first two weeks of your cycle, the temperature should be low. Then, there will be a small dip in the temperature followed by a quick rise. It will stay high for about two weeks and then it will go down again and you will get your period—unless you’re pregnant, of course! Start a fresh chart on the first day of your period.

So when are you most fertile? That little dip in temperature and sharp rise are the days you are ovulating. The days just prior to ovulation are the best for trying to conceive. Even though your chart won’t tell you when you’re ovulating until the entire cycle has been tracked, it is a great way to come to understand your cycle. “A woman then knows,” says Beltsos, “that the right things are happening and all is in order.”


Even though you know the basics of BBT now, you still may have some questions.

Do I Have to Take My Temperature Every Day?
Yes, you absolutely have to take your temperature each and every day if you are to get reliable results. If you don’t, there will be blank spots in the chart, and you will be unable to determine whether or not you are actually ovulating.

So, I Just Take My Temperature and Write It Down?
While you can just write down your temperature and leave it at that, in order to best track your fertility (and not just ovulation) you should also note any symptoms you may have. Note when you have cervical mucus and what color it is. Be sure to make note of when you are having sex, exercising, experiencing spotting, or anything else relevant. This way, once it comes time to review your BBT for the past month, you won’t have to question what might have caused a sudden spike in your temperature during a time when you shouldn’t be ovulating.

What Happens If I Still Don’t Conceive?
If you have charted your BBT faithfully for several months and attempted to conceive during your fertile window and still have not conceived, it may be time to make a visit to your doctor. There may be another issue causing your infertility that the BBT charting cannot pick up. Don’t neglect to consider male factor infertility.

If I Don’t See a Dip And Then a Spike in My Temperature, Am I Definitely Not Ovulating?
Not necessarily. You may have an irregular cycle or you may have exercised a lot, taken some medication, or even had sex causing your temperature to go haywire. If after a few months you still don’t see the dip and spike, it may be time to consult your doctor about the possibility of underlying fertility conditions.

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