Thursday, October 29, 2009

Q & A: "Basal Body Temperature (BBT) to find out when I ovulate"

Q. My husband and I have been trying to start our family for
two years now. We just started to chart the Basal Body
Temperature (BBT) to find out when I ovulate. Our doctor will
take no action until she finds out when and if I was ovulating.
We use the home predictor kits with success, but she said they
were not as effective as the BBT. Is this true? Anyway, here is
my real question: I have discovered, taking my temperature (which
usually does seem to run on the "low" side of normal, about 97.6
to 98 on average), seems to be TOO low in the mornings. I use a
digital thermometer and it has registered anywhere from 95.6 to
98 in the last few weeks that we have started charting it. It
also seems to not follow any sort of pattern. Could there be a
medical reason for lower than normal body temperature? And could
this affect fertility?
-- MM

A. Body temperatures vary a great deal. When textbooks talk
about a normal body temperature of 98.6 degrees F, that's
"normal" in the statistical sense that it is the average body
temperature. Around that number there is quite a bit of
variation. If your temperature is 97 degrees, or 96 degrees, that
is still considered within the normal range. There are medical
conditions that lower the body temperature, but it is usually
seen only in very sick individuals.

According to Tripod's consulting gynecologist Dr. Susan Yates, a
woman's body temperature will go up one-half to one full degree
at the time of ovulation, and will stay up until her menstrual
flow begins. It is caused by an increase in the amount of
circulating progesterone -- one of the hormones required for the
menstrual cycle and for maintaining pregnancy. If you are
measuring your daily basal body temperature (taken at the same
time, first thing in the morning) you should be able to detect
the increase in body temperature, but it may take a couple of
days before the effect is seen. This can lead to some frustration
in terms of trying to time intercourse in order to get pregnant
as it may already be too late. However, it is a good way for
determining whether or not ovulation is occurring.

The other test you mention is the "home predictor kit." These
kits test a urine sample for the presence of a hormone called
luteinizing hormone, or LH. LH is produced by an area of the
brain called the pituitary gland, and stimulates the ovary to
produce estrogen. In the 24 to 48 hours prior to ovulation there
will be a surge in the amount of LH, which is detectable by this
test. The more expensive tests tend to be more accurate.

The decision as to whether BBT monitoring, the home predictor
test, or both are used as part of an initial infertility work-up
is a decision best made by you and your gynecologist.

By the way, a low normal body temperature will not cause
infertility.

-- R. Jandl

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