Table of ContentsView AllTable of ContentsBasicsWhat Is BBT?How to TakeNormal BBTTracking ChangesOther Signs of OvulationBBT When PregnantFrequently Asked Questions
Table of ContentsView All
View All
Table of Contents
Basics
What Is BBT?
How to Take
Normal BBT
Tracking Changes
Other Signs of Ovulation
BBT When Pregnant
Frequently Asked Questions
This article discusses the basics of the femalemenstrual cycle, the fertile window, and how checking BBT can provide useful information for people trying to conceive or avoid pregnancy.
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How Long It Could Take to Get Pregnant
Basics of the Female Reproductive System and Fertility
Each month, hormones cause changes in the ovaries and uterus to prepare the body for potential pregnancy. The cycle begins with menstruation, the phase when the uterus sheds its lining.
On the first day of menstruation, the ovaries are busy responding to a hormone released from the brain, calledfollicle-stimulating hormone(FSH). FSH tells the ovaries to make immature eggs, calledfollicles. These follicles secrete the hormoneestrogen, which has effects throughout the body.
When estrogen rises to a certain level, it signals the brain to releaseluteinizinghormone (LH), which then triggersovulation.
During ovulation the mature egg is released from the most dominant follicle and travels through thefallopian tubesto the uterus. The leftover follicle becomes a hormone-secreting cluster of cells called thecorpus luteum, meaning “yellow body” in Latin.
The corpus luteum secretes several hormones, includingprogesterone. Progesterone causes the uterine lining to thicken in preparation for accepting a fertilized egg. Progesterone also causes changes in cervical secretions that promote sperm motility.
The Fertile WindowThe fertile window is the period in which sexual intercourse can result in pregnancy. After ovulation, the egg can live for up to 24 hours. Sperm can live in the female reproductive tract for up to five days.Having sexual intercourse in the two days leading up to ovulation has the highest chance of resulting in pregnancy, but you can become pregnant any time in the five days before ovulation and the day of ovulation.
The Fertile Window
The fertile window is the period in which sexual intercourse can result in pregnancy. After ovulation, the egg can live for up to 24 hours. Sperm can live in the female reproductive tract for up to five days.Having sexual intercourse in the two days leading up to ovulation has the highest chance of resulting in pregnancy, but you can become pregnant any time in the five days before ovulation and the day of ovulation.
The fertile window is the period in which sexual intercourse can result in pregnancy. After ovulation, the egg can live for up to 24 hours. Sperm can live in the female reproductive tract for up to five days.
Having sexual intercourse in the two days leading up to ovulation has the highest chance of resulting in pregnancy, but you can become pregnant any time in the five days before ovulation and the day of ovulation.
What Is Basal Body Temperature?
BBT is the body’s temperature when in a state of rest. In general, the body’s resting temperature is stable from day to day, but there are predictable changes in body temperature that occur at specific points in the menstrual cycle.
This information can be useful for people trying to conceive and for those trying to avoid pregnancy. People trying to conceive can use BBT topredict ovulationin order to time intercourse during the fertility window.
BBT is also a method used innatural family planningfor people who want to use abstinence or barrier contraception methods during the fertile window to decrease the chances of becoming pregnant.
How Effective Is Natural Birth Control?
How to Take Basal Body Temperature
After ovulation, the rise in progesterone levels in the luteal phase causes an increase in basal body temperature of 0.5–1 degree. If fertilization does not occur, the fall in progesterone causes the temperature to again drop to the lower level.
The changes in basal body temperature may be as small as 0.5 degrees, so it’s important to use a thermometer with accuracy to within 0.1 degrees. Anything less accurate can miss the small changes needed for fertility prediction.
Some thermometers are designed specifically for BBT that may provide some added value.
Risks of BBTNot accurate in people who have irregular menstrual cyclesIncrease in temperature occurs during or after the fertile period, so the fertile period could be missedBBT method alone is a less effective method for preventing pregnancy than other forms of birth controlBenefits of BBTInexpensiveNo side effectsDoes not involve risks of hormonal contraception
Risks of BBTNot accurate in people who have irregular menstrual cyclesIncrease in temperature occurs during or after the fertile period, so the fertile period could be missedBBT method alone is a less effective method for preventing pregnancy than other forms of birth control
Not accurate in people who have irregular menstrual cycles
Increase in temperature occurs during or after the fertile period, so the fertile period could be missed
BBT method alone is a less effective method for preventing pregnancy than other forms of birth control
Benefits of BBTInexpensiveNo side effectsDoes not involve risks of hormonal contraception
Inexpensive
No side effects
Does not involve risks of hormonal contraception
Normal Basal Body Temperature
Normal body temperature varies from person to person, but it generally ranges from 96 to 99 degrees F. Temperature varies slightly depending on how it is measured, and it can change during certain times of the day and with activity, stress, changes in sleep patterns, or illness.
How to Chart Temperature Changes
Since the increase in BBT occurs at or after ovulation, the fertile period begins several days before you notice a drop in temperature. In other words, you can become pregnant in the week leading up to an increase in temperature. However, charting your temperature over time can provide information about the timing of your cycle to predict fertility in future months.
When measuring BBT, the body should be completely at rest. Keep a thermometer within reach at your bedside so you can take your temperature immediately upon waking, before getting out of bed, or doing any activity.
Tools to Track BBTOther than a thermometer, all you need is a pen and paper to plot your temperature on a graph or table each day. Also, several phone apps have been designed specifically to plot BBT and provide insight into your cycle and fertile window.
Tools to Track BBT
Other than a thermometer, all you need is a pen and paper to plot your temperature on a graph or table each day. Also, several phone apps have been designed specifically to plot BBT and provide insight into your cycle and fertile window.
BBT is one of several signs you can use to track your fertile window.
Hormones cause several other changes in the body. A combination of fertility awareness methods can be used for those trying to conceive to time intercourse, or they may be combined with barrier contraception or abstinence during the fertile period to avoid pregnancy. Methods include:
Basal Body Temperature When Pregnant
The hormone changes that occur with pregnancy also affect BBT. A couple of findings on the BBT chart can be early signs of pregnancy. Of course, suspected pregnancy should be confirmed with a pregnancy test and a visit to your healthcare provider.
One very early potential sign of pregnancy is a one-day drop in temperature, called the implantation dip. An implantation dip is not the most reliable sign of pregnancy because it may not be present. If it’s present, it does not always mean pregnancy.
The dip can occur about a week after ovulation if fertilization has occurred and lasts for just one day. Compare this to a typical cycle when a dip will be seen just before the onset of your period and will remain low until the next time you ovulate.
A more predictable and noticeable change in BBT that can indicate pregnancy is a prolonged increase in temperature. During pregnancy, progesterone levels remain high and cause a sustained increase in BBT.
Look for otherpregnancy signs, like a missed period and symptoms like fatigue and nausea.
Implantation: Timing of Early Pregnancy Symptoms
Summary
Basal body temperature is a noninvasive, inexpensive, and simple measure that can be used to track fertile periods for those trying to conceive or avoid pregnancy. BBT relies on charting daily temperature and noticing small changes over time to predict future fertility windows.
A Word From Verywell
Not everyone is able to reliably predict ovulation, particularly those who have irregular menstrual cycles. Speak with your healthcare provider with any concerns you have about infertility or choosing the right form of birth control.
Frequently Asked QuestionsBasal body temperature drops when your period starts because of the decline in progesterone levels. If basal body temperature remains elevated and you miss your period or only have light spotting, take a pregnancy test.The fertile window is based on how long sperm and a released egg can survive in the female reproductive tract. Sperm can survive for up to five days. A released egg can survive for up to 24 hours after ovulation. Adding these together give you a fertile window of approximately six days.A persistent increase in basal body temperature can indicate pregnancy due to higher progesterone levels, but this should not be the only sign you rely on. It will coincide with a missed period (or very light spotting from implantation bleeding). Always confirm suspected pregnancy with a pregnancy test.
Basal body temperature drops when your period starts because of the decline in progesterone levels. If basal body temperature remains elevated and you miss your period or only have light spotting, take a pregnancy test.
The fertile window is based on how long sperm and a released egg can survive in the female reproductive tract. Sperm can survive for up to five days. A released egg can survive for up to 24 hours after ovulation. Adding these together give you a fertile window of approximately six days.
A persistent increase in basal body temperature can indicate pregnancy due to higher progesterone levels, but this should not be the only sign you rely on. It will coincide with a missed period (or very light spotting from implantation bleeding). Always confirm suspected pregnancy with a pregnancy test.
3 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Simmons RG, Jennings V.Fertility awareness-based methods of family planning.Best Pract Res Clin Obstet Gynaecol. 2020;(66):68-82. doi:10.1016/j.bpobgyn.2019.12.003Su HW, Yi YC, Wei TY, et al.Detection of ovulation, a review of currently available methods.Bioeng Transl Med. 2017;2(3):238-246. doi:10.1002/btm2.10058Fertility Friend.Implantation dip study.
3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Simmons RG, Jennings V.Fertility awareness-based methods of family planning.Best Pract Res Clin Obstet Gynaecol. 2020;(66):68-82. doi:10.1016/j.bpobgyn.2019.12.003Su HW, Yi YC, Wei TY, et al.Detection of ovulation, a review of currently available methods.Bioeng Transl Med. 2017;2(3):238-246. doi:10.1002/btm2.10058Fertility Friend.Implantation dip study.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Simmons RG, Jennings V.Fertility awareness-based methods of family planning.Best Pract Res Clin Obstet Gynaecol. 2020;(66):68-82. doi:10.1016/j.bpobgyn.2019.12.003Su HW, Yi YC, Wei TY, et al.Detection of ovulation, a review of currently available methods.Bioeng Transl Med. 2017;2(3):238-246. doi:10.1002/btm2.10058Fertility Friend.Implantation dip study.
Simmons RG, Jennings V.Fertility awareness-based methods of family planning.Best Pract Res Clin Obstet Gynaecol. 2020;(66):68-82. doi:10.1016/j.bpobgyn.2019.12.003
Su HW, Yi YC, Wei TY, et al.Detection of ovulation, a review of currently available methods.Bioeng Transl Med. 2017;2(3):238-246. doi:10.1002/btm2.10058
Fertility Friend.Implantation dip study.
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