basal body temperature early pregnancy

What is your basal body temperature in early pregnancy

Basal body temperature (BBT) is your morning body temperature before you get out of bed. Charting this temperature over the course of your menstrual cycle is an inexpensive, low-tech way to help determine if you’re ovulating. Because ovulation disorders are one of the major causes of female infertility, many OB/GYNS recommend BBT charting to patients when they first start trying to conceive. This way, doctors can identify and treat any ovulation problems as early as possible.

Contrary to popular belief, BBT charting is not the most effective way to time sexual intercourse for conception. Your fertility is highest during the several days preceding ovulation and the day it occurs, but the change in BBT that indicates ovulation happens 12 to 24 hours afterwards. So BBT doesn’t predict ovulation, but tells you that it happened. If your cycle is regular, tracking your BBT for a couple of months will give you a good idea of when in your cycle you ovulate.

How does measuring BBT help detect ovulation?

A woman’s normal non-ovulating temperature is between 96 and 99 degrees Fahrenheit, depending on the individual. Following the release of the egg, BBT increases by about half a degree in almost all women. The hormone progesterone, secreted by the ovary after ovulation, heats things up; it also prepares the uterine lining for a possible pregnancy. Body temperature will remain roughly half a degree higher until right before menstruation, when it will return to normal. (If you get pregnant, your temperature will stay higher through the first trimester). If your temperature doesn’t follow this pattern, it might indicate an ovulation problem.

Detecting the change

Because the spike in body temperature at ovulation is so small, you need a special basal thermometer (available in drugstores) to measure it. A basal thermometer records temperatures in one-tenth of a degree increments instead of the two-tenth increments on fever thermometers.

Basal thermometers come in mercury and digital versions. The mercury BBT thermometers look like fever thermometers, except the divisions between degrees are large and easy to read. These thermometers can be used orally or rectally. Digital BBT thermometers also look like fever models, except they boast special features like an illuminated display (for easier reading on dark mornings). The digital thermometers are used orally. Most thermometers come with several graphs so you can chart your BBT over two to three cycles.

If you don’t detect an ovulation-indicating temperature rise after several cycles, your doctor will give you a blood test to confirm the findings. BBT thermometers are not 100 percent accurate, and some women ovulate even without an increase in temperature. False readings can be caused by a variety of things, including waking up at different times in the morning. Here’s how to get the most accurate results:

• Take your temperature when you first wake up and are lying or sitting quietly in bed. You need to do the reading at the same time, give or take 30 minutes, every morning.

• Leave the thermometer on your night table before you go to bed so there’s no need to get up for it in the morning. Shake mercury thermometers down at night or dip them briefly in cool water. Doing the motions in the morning can cause a rise in temperature.

• Don’t eat or drink anything, even water, before doing the reading.

• Be aware of factors other than ovulation that can increase BBT: emotional disturbance, stress, a cold or infection, jet lag, drinking alcohol the night before, using an electric blanket.

• Don’t pull all-nighters: You need to have at least three hours of uninterrupted sleep to get an accurate reading.

Please note: The Bump and the materials and information it contains are not intended to, and do not constitute, medical or other health advice or diagnosis and should not be used as such. You should always consult with a qualified physician or health professional about your specific circumstances.

If you are trying to get pregnant, you may have heard about charting your basal body temperature, which is part of natural family planning, a method for detecting when the body is most fertile to either become pregnant or avoid pregnancy. The concept is that a person monitors their body temperature and charts the daily results to find out whether ovulation has occurred. Conversely, people who are trying to avoid pregnancy may attempt to use basal body temperature to inform their choices surrounding unprotected sex as well.

But just how effective is using basal body temperature for fertility purposes? To answer this question, it’s important to know exactly what basal body temperature is, including what makes it change and why a person would chart it.

Basal body temperature is defined as the body’s core temperature, explains Elizabeth McGee, M.D., director of the reproductive endocrinology and fertility division at the University of Vermont Larner College of Medicine.

Many factors can affect a body’s temperature, including diet, the environment, physical exercise and even stress, continues Dr. McGee, but basal body temperature refers to your temperature when your body is completely at rest.

Unless someone is sick, their body temperature doesn’t change much; fractions of degrees may fluctuate throughout the day without a person even noticing, explains Dr. McGee. However, even if it’s not noticed, body temperature does indeed rise and fall at certain times throughout the menstrual cycle, and this is exactly why some people chart basal body temperature as a natural family planning tool.

How Is Basal Body Temperature Related to Fertility?

There are two overarching phases in the menstrual cycle, according to Lusine Aghajanova, M.D., a clinical assistant professor of obstetrics and gynecology at Stanford and an infertility specialist. The two phases are:

The follicular phase: known as “pre-ovulation”
The luteal phase: known as “post-ovulation”

Here’s where basal body temperature comes in: You can use basal body temperature as a natural family planning method because a person’s fertile window is six days before ovulation. By tracking cycles and learning when ovulation happens in your cycle over the course of a few months, you can optimize the timing of trying to increase chances of conception. Each morning, you can write down your basal body temperature in a notebook as a way of tracking it. Since body temperature is higher—even though it’s slight—after ovulation, this will help to know when you’re ovulating each month.

While charting basal body temperature can provide helpful intel, both experts explain that a change in temperature is not detectable right away. “The rise in temperature is measurable one to two days after ovulation occurs,” says Dr. Aghajanova. In other words, it’s a retrospective clue. “It’s not a prospective indicator that a woman is going to ovulate; with basal body temperature, it confirms that you have ovulated.” This means that while charting basal body temperature can be a helpful way to see when you’re ovulating each month, a rise in temperature shouldn’t be an indicator that someone is currently in their most fertile window. “It will be too late,” says Dr. Aghajanova.

Instead of using a slight rise in temperature as an in-the-moment way to detect the most fertile window, what can be more beneficial is charting basal body temperature over time to see when ovulation is likely to occur. That way, you can become more aware of when you will be in your luteal phase each month, the most fertile part of your cycle.

Charting basal body temperature could also be a way to detect early pregnancy. If a basal body temperature remains high, it may be a sign that you’re pregnant since progesterone levels remain elevated through pregnancy.

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What Makes Basal Body Temperature Change?

Basal body temperature increases during the luteal phase, but why?

Dr. McGee explains that during the luteal phase, the hormone progesterone rises, staying at this increased level until the uterine lining begins to shed. (In other words, when a person starts menstruating.) Dr. Aghajanova adds that this rise in progesterone is what leads to an increase in body temperature. “The increase is very small, just half a Farenheight degree, [0.3 degrees Celsius],” she says.

If a person becomes pregnant, Dr. Aghajanova continues, progesterone levels will remain elevated, as will her temperature. If pregnancy does not occur, the temperature will decrease.

Both experts say that there are other factors that can increase body temperature as well. “Eating or drinking, moving your body, weather, sickness and stress can all affect body temperature,” says Dr. McGee. The many factors that influence a body’s temperature are another reason why basal body temperature isn’t the most accurate way to track fertility, she notes.

How to Track Basal Body Temperature

While neither expert advises using basal body temperature as a primary tool for becoming pregnant or avoiding pregnancy, it can be used as an indicator of ovulation or as a way to detect early pregnancy. But since so many factors affect body temperature aside from hormone levels, both doctors emphasize that there needs to be consistency in tracking.

“Tracking basal body temperature is quite cumbersome,” says Dr. Aghajanova. “You must take your temperature using a thermometer first thing in the morning before getting out of bed, before drinking or eating anything or exposing yourself to an environment where hot or cold [weather] may change your temperature. You should not have sex, brush your teeth or do anything else before taking your temperature.”

To properly track basal body temperature, it must be done every day at the same exact time, she advises. Each morning, record your temperature so you can see a pattern throughout the month, especially during and immediately after the luteal phase.

When to See a Doctor

If you are tracking your basal body temperature and it has remained elevated, this could be a sign of early pregnancy. A pregnancy can be confirmed with a home pregnancy test. If you are pregnant, plan your first prenatal visit in order to receive proper care.

If you’re curious about basal body temperature because you’re trying to conceive, an obstetrician-gynecologist or fertility specialist can offer other ways to track fertility that may be more effective. If you are under 35 and been having unprotected sex regularly for six months or longer and have not become pregnant, seeing a fertility specialist can be beneficial to help find out why, explains Dr. McGee.

Charting basal body temperature can be a helpful tool to help you figure out when you’re ovulating each month and to pinpoint when you’re in the luteal phase, the most fertile window. However, because many factors can affect temperature, it shouldn’t be the only method used to prevent pregnancy or to get pregnant. It could also help detect early pregnancy, although this should be confirmed with a pregnancy test.

If you have any questions about either preventing pregnancy or getting pregnant, it’s beneficial to talk to your doctor who can provide information on what to do in addition to charting your basal body temperature.

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