Fertility Awareness Method: Basal Body Temperature Charting

Basal body temperature (BBT) is the body temperature at rest. It is measured immediately after awakening and before any physical activity has been undertaken. This measurement is very important for fertility awareness among women. How? Let’s find out.

How BBT estimates the day of ovulation

Monitoring BBT is one way of estimating the day of ovulation as it causes an increase of one-half to one degree Fahrenheit (or one-quarter to one-half degree Celsius).

Charting a women’s BBT is a useful tool for couples trying to conceive because of its ability to confirm ovulation. This also helps the couple understand more fully the physiological processes surrounding ovulation. For one, not all women ovulate 14 days before their next menstruation period.

In fact, for a lot of women, the time between ovulation and their period (or luteal phase) is shorter, around 10 days.

What causes changes in BBT

The higher levels of estrogen present during the pre-ovulatory phase of the menstrual cycle lower BBTs. Meanwhile, the higher levels of progesterone released by the corpus luteum (a temporary endocrine structure in the ovary that secretes progesterone and estrogen) and after ovulation raise BBTs.

The rise in temperatures can most commonly be seen the day after ovulation, but this varies and BBTs can only be used to estimate ovulation within a three day range.

If pregnancy does not occur, the disintegration of the corpus luteum causes a drop in BBTs that roughly coincides with the onset of the next menstruation. However if pregnancy does occur, the corpus luteum continues to function and maintain high BBTs for the first trimester of the pregnancy.

How to monitor BBT

A woman’s BBT is taken orally with a special BBT thermometer, or any thermometer that displays the one-tenth degree increments. The BBT must be taken before any activity, first thing in the morning, after at least three hours of consecutive sleep.

The thermometer must be shaken down the night before, because even this simple activity before measuring your BBT could actually raise her temperature. Once she have read her temperature, mark it on a special BBT chart to monitor her progress.

Is BBT charting enough

Not exactly, as it would only tell you when ovulation has already occurred. This means that is the egg can only live about 12 to 24 hours, and by the time her temperatures rise a day or two after ovulation, the eggs will already be gone.

When charting a woman’s fertility signs in order to time the couple’s intercourse, it is most useful to also chart her cervical fluid to determine when she is in her most fertile phase.

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