Basal Body Temperature

Human body temperature (for oral measurement) is said to be normal when the reading is between 98.2 ± 1.3 °F or 36.8 ± 0.7 °C. Slight variations are considered as normal. You must have noticed that the body temperature is not constant throughout the day or night. It increases during physical activity. The body attains lowest temperature when you are resting (usually during sleep). This lowest temperature is known as basal body temperature (BBT).

Since it is not possible to measure the true BBT while sleeping, it is generally measured immediately after waking up in the morning, before getting out of bed (before starting any activity). This reading can be closest to the true BBT attained during sleep, though it may be slightly higher than the true lowest temperature attained by your body. You can measure the BBT with normal thermometer or with a basal thermometer which tracks your body's minutest temperature shift.

Basal Body Temperature and Conception

Women can notice a slight rise in BBT after ovulation. Hormonal changes bring about an increase in BBT. A woman is most fertile near ovulation and this 'fertile time' can be identified by keeping a record of BBT for the whole month. You can make a chart for yourself and easily find out the time of ovulation for yourself.

While determining the most fertile time to get pregnant, you need to consider certain important factors. The egg released by the ovaries is available for fertilization for 24 hours only. Though the sperms are viable for 2-3 days, after entering into the vagina; fertilization is possible only if the sperms come in contact with the egg within 24 hours after its release. Ovulation usually takes place in the middle of the cycle (on the 14th day); if the woman has a normal menstrual cycle of 28 days. If the cycle lasts for 30 days, ovulation may occur on 16th day. The most fertile time for a woman depends upon the length of her menstrual cycle, age, overall health, etc. If you want to avoid pregnancy, you should avoid unprotected sex 3-4 days before and after ovulation. Remember, BBT cannot predict ovulation. Slightly higher BBT shows that ovulation has taken place.

Women who have irregular menstrual cycles may ovulate regularly. Similarly, those who have regular menstrual cycles can be actually anovulatory (having a luteal phase). Women undergoing infertility treatment need to keep a record of their BBT by preparing a chart. Having unprotected sex during ovulation increases the chances of pregnancy. Women are expected to monitor the graph of BBT over a span of three months. Then they can get an idea of their 'most fertile time' during the menstrual cycle.

You are supposed to note down your BBT from the first day of your period. The mid-cycle surge in temperature (most probably on 13th -14th day) indicates ovulation time. If you conceive, temperature remains elevated for the first trimester of the pregnancy. If you don't conceive, BBT drops which indicates an onset of next menstruation. BBT charting also helps find out whether the length of the post-ovulatory (luteal) phase of your menstrual cycle is adequate to sustain a pregnancy. As BBT helps know the period of ovulation, the woman can perform pregnancy test 1-2 weeks after ovulation. Early testing can give false negative results.

Higher estrogen levels in the phase before ovulation lead to low BBT. Higher progesterone levels after ovulation result in an increase in BBT. After the first trimester, when the placenta starts functioning like the corpus luteum, the BBT drops down to its pre-ovulatory normal level. Certain unusual conditions like a cyst in the corpus luteum can keep BBT elevated. This can prevent menstruation. The cyst may require weeks or months to resolve. But such condition is quite rare.

Experts say that 18 consecutive days of elevated basal body temperature can be considered as one of the early signs of pregnancy. BBT charting helps estimate gestational age of the fetus. I hope you found the information regarding the significance of BBT tracking helpful.