Basal body temperature (BBT) is the body temperature while at rest. After ovulation, the ovary produces progesterone which causes a woman’s BBT to rise.
If you’ve been trying to conceive for several months without luck, you may have considered fertility charting. Charting is an effective way to monitor your fertility by taking your daily temperature and noting other cycle changes, such as increases in cervical mucus.
Your fertility is highest during the two days before ovulation and the day it occurs, according to Parenting Magazine. However, your BBT does not change until 12 to 24 hours after ovulation.
“If there is no pregnancy, your temperature will stay elevated for 10-16 days, until the corpus luteum regresses,” according to Fertility Friend. “At this time, unless there is a pregnancy, progesterone levels drop dramatically and you get your period.” When you finally get your period, your temperature may drop again.
What the Experts Say
Your basal body temperature is your “base” temperature typically taken during a full resting state. To maintain an accurate chart, most experts recommend taking your BBT in the morning directly after waking and before getting out of bed.
The basal body temperature method is based on the principal that your body begins to “warm” about 48 hours after ovulation.
However, it’s important to note that not all women will experience this thermal shift. While some ladies will have a quick spike in their BBT shortly after ovulation, others will notice a gradual temperature shift that occurs over the course of several days.
This often means that it took longer than normal for progesterone levels to rise, or that the body responded slower than normal to rising progesterone levels.
Here’s what some experts have to say about changes in BBT following ovulation:
“Just before ovulation, a woman’s BBT typically drops a few fractions of a degree. After ovulation, the BBT usually rises between 0.4 and 0.8 degrees F and remains at that higher level every day until just before menstruation begins.”
Suzanne Wymelenberg, Beverly Winikoff, The Whole Truth About Contraception
“Over two or three months, the typical chart of an ovulating woman will show a pattern of a slight temperature rise (0.4 to 1.0 degrees F) at mid-cycle. The rise in temperature remains fairly level until about the time of menstruation, at which point the temperature drops. This is called a biphasic pattern and is a good indication that you ovulated.”
Joan Liebmann-Smith, The Unofficial Guide to Getting Pregnant
“Remember, the basal body temperature refers to the body temperature after a night of normal, restful sleep. The body temperature normally reaches its lowest levels after all mental and muscular activity has ceased for several hours. This is why the best time to record this basal temperature is upon awakening. Your temperature during the rest of the day is affected by your daily activities and will not be an accurate reflection of whether or not you are making progesterone.”
Sherman J. Silber, How to Get Pregnant
“Temperature will vary slightly from day to day, but at the time of ovulation, or just before, there will be a marked rise (at least 0.4 F) in the average temperature from one day to the next. This means that it is possible – in retrospect – to know that the fertile period is over once there have been at least 3 consecutive days of the higher average temperature.”
Karen J. Carlson, The New Harvard Guide to Women’s Health
“At the time of ovulation, the BBT can be seen to dip slightly (about 0.5 F), is then rises to a level no higher than normal body temperature, and then stays at that level until 3 or 4 days before the next menstrual cycle. This increase in BBT marks the time of ovulation, because it occurs immediately after ovulation.”
Adele Pillitteri, Maternal and Child Health Nursing
What Can My BBT Chart Tell Me?
By looking at your BBT chart, you can help determine if you are ovulating and when you should time your intercourse for the best odds of conception. You can also learn the average length of your menstrual cycle, whether your cycles are regular or irregular, and if you might be pregnant.
Fertility awareness methods (FAMs) include the temperature method, cervical mucus method, and the calendar method to track fertility signs. FAMs are approximately 76 to 88 percent effective, according to Planned Pregnancy, meaning every 12 to 24 out of 100 couples who use FAMs will fall pregnant each year.
How Long Will My Temperature Stay Up?
On average, your BBT will remain elevated for around 14 days. “A woman’s normal non-ovulating temperature is between 96 and 99 degrees Fahrenheit, depending on the individual,” says Parents Magazine. “Following the release of the egg, BBT increases by about half a degree in almost all women.”
If you become pregnant during your cycle, you may notice that your BBT remains elevated for up to 18 days or more after ovulation. When pregnancy is successful, it’s also common to see a triphasic chart which shows three distinct temperature rises that may indicate conception has occurred.
What Factors Can Affect My BBT?
If you have been charting for a while and your chart seems off, there may be a reason. Various factors can influence the results of your basal body temperature, making it more difficult to detect the time of ovulation. The most common factors that affect BBT include fever, infections, colds, medications, alcohol, smoking, stress, travel, and breastfeeding.
Charting is an easy and effective way to identify changes in your cycle. By taking note of when your BBT rises and falls, you can help pinpoint ovulation and increase your odds of pregnancy.