Basal Body Temperature To Track Fertility
Hopeful parents might enhance their chances of becoming pregnant by
preparing a basal body temperature, or BBT, chart to identify the
woman's ovulation cycle. By knowing the ovulation cycle, the couple can
judge when coitus, or sexual intercourse, is more likely to result in
BBT is the lowest temperature of the body after waking and before
physical activity. Even though the temperature is measured upon waking,
it is a bit higher than the average BBT. A BBT thermometer is needed to
take accurate BBT readings because the specialized device records body
temperature to one tenth of one degree.
A woman's body temperature decreases during the first part of the
menstrual cycle. Typically, BBT then rises during ovulation and remains
higher throughout the second part of the cycle, just before the
menstrual flow begins. Recording BBT daily will show when ovulation
probably occurs. During ovulation, BBT increases 0.5 to 1.0
ºFahrenheit (0.25--0.50 ºCelsius). A woman has a
lower temperature before ovulation and a higher temperature afterwards.
This is known as a biphasic pattern. Using a BBT thermometer, the
pattern can be used as a tool to determine fertility rate.
BBT registers when the body is completely at rest. If measured orally,
BBT may register around 96--98 ºF (35.5--36.6 ºC).
Before ovulation, a temperature of 97--99 ºF (36--37
ºC) is considered normal. Temperature fluctuations occur by
fractions of a degree, typically 0.1--0.5 degree. As the woman begins
to learn more about her body by charting temperatures daily, she will
recognize patterns of rising and falling temperature. Changes can occur
either suddenly or gradually and may vary each cycle.
To be able to gather reliable and meaningful BBT readings, it is
important to take the temperature at the same time every day. Even with
lack of sleep from frequent upsets during the night, the woman should
take her temperature at the same time. Also, keep in mind that if the
temperature is being taken orally, eating and drinking affect
temperature for a certain period of time, so take temperatures before
eating food or drinking anything.
Another way of describing the average temperature is "coverline." Body
temperature during ovulation should stay above the coverline for a
little less than two weeks, or approximately 12 days. A temperature
lower than the coverline may indicate a short luteal phase defect or
Timing of coitus is also affected by the fact that sperm can fertilize
an egg two or three days after intercourse. In some instances sperm can
remain active for five days or more. The woman can become impregnated
from intercourse several days before ovulation. Thus, the combination
of the life duration of sperm and BBT thermometer may improve pregnancy
In addition to charting BBT, the woman should be looking for signs of
pregnancy. A high temperature for 18 consecutive days could indicate
fertilization of the egg. A third rise in temperature, about seven to
10 days after ovulation, is called a triphastic chart. This may
indicate pregnancy, even though this is not a definite sign. Some women
who experienced a triphasic chart have not become pregnant.
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