The Link Between Body Temperature, Ovulation, and Pregnancy
You may have heard that your body temperature can somehow tell you whether you are ovulating or pregnant. You're intrigued, and now you want to know more. The good news is that it's true! Ovulation and pregnancy both affect your body temperature, and charting your temperature daily can reveal whether these events occur. Charting your body temperatures can also reveal weakened hormones or other health concerns, affecting your fertility and the length of your cycles.
Keeping track of your daily body temperature is useful information to those who simply want to know more about their cycles, those who wish to avoid pregnancy, and those who are trying to achieve pregnancy.
Male and Female
When a woman's body is maturing egg cells, the body is cooled by the affects of estrogen. Likewise, when a man's body is maturing sperm cells (which is all of the time!), they are cooled by the scrotum, which removes the testicles away from the heat of the body. It seems these cells like to mature a little cooler than all other cells in the body!
Phases of the Female Cycle
In order to understand the link between your body temperature and ovulation, you'll also need to know a little bit about the female menstrual cycle. A new cycle begins with menstruation (having your period), which is the result of your hormones dropping after the previous cycle.
After your period, the pituitary gland in your brain sends hormones to the ovaries to begin ripening a few egg cells. Egg cells are each kept in their own follicle in the ovary, and thus the hormone that begins to ripen them is called Follicle Stimulating Hormone (FSH). This phase of the cycle is called the Follicular Phase. As these follicles ripen, they release Estrogen. This hormone has a cooling effect on the body and lowers your overall temperature.
The estrogen created by the ripening eggs eventually triggers the pituitary gland to create Luteinizing Hormone (LH), which in turn causes the most mature egg to burst from the ovary, known as ovulation. The body is now in the Luteal Phase, which lasts only 12-16 days in a healthy individual. Within 24 hours of ovulation, the burst follicle (now known as the corpus luteum) begins producing the hormone Progesterone. As opposed to estrogen, Progesterone has a warming effect on the body and raises your internal temperature.
Now if pregnancy does not take place, then the progesterone-emitting follicle will die after 12-16 days and the hormone levels will fall (along with your temperature), causing the body to shed the uterine lining during menstruation. If pregnancy does occur, then the fertilized egg produces hormones to begin the the process of pregnancy. When an egg is fertilized and pregnancy takes place, your body temperature remains raised at or higher than levels during the luteal phase.
So, your body temperature is affected by your cycle in these ways:
- Estrogen cools the body temperature before ovulation
- Progesterone warms the body temperature after ovulation and until menstruation
- Pregnancy will maintain the warmer body temperature until birth
How Long are the Two Phases?
The Follicular Phase (pre-ovulation) has great variability in how many days it can last. Many factors such as stress, health, and diet can affect its length. It can range from being less than two weeks long to being several months long, and change from cycle to cycle. This is the number one reason why many women have "short", "long", or "missed" cycles. (They're not missing cycles at all, really, just experiencing very long cycles).
The Luteal Phase (post-ovulation), on the other hand, is much more consistent. A healthy luteal phase is always between 12-16 days long. The lifespan of the egg cells and the follicle dictate this, and is common to all women. Shorter luteal phases indicate poor hormone levels, and longer ones either indicate pregnancy or ovarian cysts.
Warm or Cool: It's all Relative
So what does it mean that these hormones "warm" and "cool" your body temperature? While 98.6 Fahrenheit is often cited as the human body temperature, it is just an average daytime temperature. Some people's temperatures are a little lower or a little higher than 98.6, and it varies a little day by day, depending on your health, sleep, cycle, and activities.
The best way to keep track of your temperature is to chart your basal body temperature. This is your body's temperature as soon as you've woken from a night's sleep. Every night your body temperature dips, and taking your temperature the moment you awake will avoid many factors that change your temperature during the day, such as eating, activity, stress, bathing, and more. Without these daytime activities to complicate your charts, you can easily see your temperatures rise and fall with your cycle.
Each day your temperature will vary within a few tenths of a degree. During a given phase however, whether follicular or luteal, there will be a noticeable range that your temperature tends to stay in. Then, when you switch into a different phase, the temperatures will move into an entirely different range of temperatures. Even though any given day may be slightly higher than the one before, ALL the days in the luteal phase will be higher than ALL the days in the follicular phase, with few exceptions. Take a look at the chart below to see how the daily changes differ from the change in range between the two phases.
- When the luteal phase begins at ovulation, your temperature will rise and remain high for 12-16 days. A single day with a high temperature does not indicate ovulation.
- When the follicular phase begins with menstruation, your temperatures will drop and remain low.
- The change in temperature is clear enough that a horizontal "cover-line" can be drawn, separating the two ranges of temperatures
Sometimes there are a few days with higher temperatures during your period due to residual hormones from the last cycle, but these will fall again as soon as bleeding ends. The follicular phase will then remain cool until ovulation.
A chart showing clear change in temperature at ovulation and menstruation
To draw a cover-line like you see above and distinguish between the temperatures of the follicular and luteal phases, follow these steps:
- Identify the day your temperature rises at least two tenths of a degree higher than the previous six days.
- Count back the six days before the rise, identify the highest day of those six, and draw a horizontal line one tenth of a degree above it. This cover-line will change slightly from cycle to cycle.
- With few exceptions, the luteal phase will remain above this cover-line. If it does not, then you may have misidentified the day of ovulation.
Anovulation is the absence of ovulation, where an egg is not released and the hormones do not enter the luteal phase. Anovulation is essentially a prolonged follicular phase.
Anovulation may or may not occur with Amenorrhea, which is the absence of menstrual bleeding. Some women can go months without experiencing a "period", although they are not pregnant. Many health issues and hormonal imbalances can result in amenorrhea.
Not all women realize, however, that having an apparent "period" does not guarantee that ovulation has taken place. If a woman is anovulatory, her hormones can still periodically weaken, resulting in the shedding of the uterine lining as a "period". Or the prolonged follicular phase builds the uterine lining until it cannot structurally support itself, and it breaks down. These are not true "menstrual periods" because a full cycle has not taken place. Without any other information, however, these women believe they are having periods and may not realize that they might be anovulatory.
Charting your basal body temperature is the best and easiest way to determine if you are ovulating. If you find or suspect that you are anovulatory, your chart will not show a clear and sustained rise in temperatures, whether or not you are experiencing apparent "periods". Tracking your temperature may relieve some of the uncertainty for women who have irregular periods or very long cycles by providing a little bit of insight into what is going on. If you are concerned about your fertility, then discovering an anovulatory chart can signal a need for dietary changes or a health check-up.
- Anovulation can be identified in a chart with no clear and sustained rise in temperatures.
- Anovulatory cycles can result is seemingly regular "periods", or last for months with irregular or no periods.
- Improving diet and health can strengthen your hormone levels so that ovulation naturally occurs again
An anovulatory chart showing no clear or sustained change in temperature
Any luteal phase lasting longer than 16 days indicates pregnancy. Rarely, however, a longer luteal phase may occur with the presence of an ovarian cyst that continues to emit progesterone. If your luteal phase has lasted longer than 16 days but a pregnancy tests reads "negative", wait a few days and take another test. If it still reads negative, a gynecologist can perform an ultrasound and determine if pregnancy or an ovarian cyst is lengthening your luteal phase. Many cysts resolve on their own, others may require intervention.
Temperature and Pregnancy
Remember that I said the luteal (post-ovulation) phase only lasts 12-16 days? This fact is common to all women, and only severe hormonal imbalances will change it. A luteal phase that lasts longer than 16 days almost certainly means that the woman is pregnant. Rarely, an ovarian cyst can cause the luteal phase to lengthen.
If pregnancy occurs, your body temperature will remain raised because the fertilized egg creates progesterone and the hormone human chorionic gonadotropin (HCG), keeping you warm, building the uterine lining, and preventing menstruation. Your temperature will remain raised until the end of the pregnancy.
Often pregnant women will experience a "tri-phasic" temperature shift, where there are three distinct temperature ranges, rather than the typical two. The "third" temperature phase usually occurs when the fertilized egg implants in the uterus, about a week after ovulation, and is likely due to the increased hormones that are being produced. The tri-phasic pattern is not a necessary symptom of pregnancy and does not always occur. If you see this distinct temperature shift and your temperatures remain high for more than 16 days, then you can be sure of pregnancy. The colored chart below shows this pattern.
- Any luteal phase (with raised temperatures) that lasts longer than 16 days indicates pregnancy
- Sometimes a "tri-phasic" temperature pattern will be apparent with pregnancy
Temperature charts showing pregnancy
Can I take my temperature and know if I am pregnant?
No! Remember, "high and low" is completely relative, and you need context to know what your temperature is telling you. You cannot take a single temperature one day and determine if it is "high" or "low".
Furthermore, even if you are convinced your temperature is "high", you will not know if it is high merely because you are in your post-ovulation, luteal phase (but not pregnant!) or if the luteal phase has continued into pregnancy. Nor can you determine that your period is "late" unless you have charted your entire cycle. Cycles can easily vary from the past, and unless you track your temperatures you will not know if it's due to a prolonged follicular phase or due to pregnancy. You need to have been charting your temperature throughout your cycle to accurately use it to determine your current state.
If you have not been charting your temperatures but suspect you are pregnant, take a pregnancy test or visit your gynecologist.
What Else Can Your Temperature Tell You?
Besides ovulation and pregnancy, there are a few other things that charting your basal body temperature can tell you.
- Low temperatures, below about 97.5 and into the 96's, usually indicates hypothyroidism.
- Very high temperatures might indicate hyperthyroidism, adrenal issues, or other health issues.
- Predicting when you will menstruate: this only works for women who are ovulating. Once you have ovulated, you know that you will menstruate in 12-16 days (assuming pregnancy does not occur).
- Low hormone levels: you will see this as luteal phases that are shorter than 12 days, prolonged follicular phases, or anovulatory cycles. Low hormone levels may make it more difficult to become pregnant and/or increase the risk of miscarriage.
Find a Basal Thermometer to Start Charting:
Learn About FA & Charting
How To Keep Track of Your Temperature
Charting your basal body temperature is really very easy. Find a thermometer that is specifically labeled "basal". These thermometers have a shorter range (typically stopping around 100 degrees) but are more accurate within that range. Keep this thermometer at your bedside and get into the habit of taking your temperature as soon as you've woken up, while you are still laying down. Try to take it at the same time every day. It's okay if you forget to some days in the beginning, as long as you are committed to remembering it in the long run. If you wake up to an alarm clock, place the thermometer next to or on the alarm so that it is right next to your hand when you turn off the alarm. Do whatever makes sense to your wake-up routine.
If you want to chart your temperatures, I suggest looking into the Fertility Awareness Method. This method will lay out all the rules on how to recognize ovulation and other conditions through your temperatures, plus many more signs. Fertility Awareness is a method where you gather daily information and use it to be aware of your cycle and fertility. This method can be used simply for information purposes, or to help prevent or even achieve pregnancy. By learning Fertility Awareness you will learn a lot more about your body and cycle than is written in this article. Even if you choose to only look at your temperatures, FAM is a very helpful tool. The article on the right is an introductory article on FAM for those who would like to learn more.
If you would like to start tracking your temperatures, use the other article on the right to find a chart that works for you.
- Use a basal body thermometer to take your temperature every morning, as soon as you've woken up.
- Use a chart from the article on the right to records your temperatures.
- Day 1 is the first day of your period, where bright red blood is present. When your next period begins, start a new chart with Day 1.
- If ovulating, draw a cover-line according to the steps written previously in this article. The cover-line should be one tenth of a degree higher than the six days preceding the rise (ovulation).
- If ovulation has occurred, the following days will remain above the cover-line. If they do not, then you have either not ovulated, or are seeing the symptoms of poor hormone levels. Turn to Fertility Awareness for explanations of confusing cycles.
- Pregnancy is indicated by luteal (higher temperatures) phases lasting longer than 16 days. Always confirm pregnancy with a test or a visit to your gynecologist.