A
standard chart with the cover line drawn.
When drawing your cover line, if you have one temperature in the first half of your cycle that is much higher than all the others (more than the 0.2°F rise you’re looking for), consider it a fluke and ignore it when working out where to draw the cover line and when you ovulate. We call this the “rule of thumb”—put your thumb over the temperature that’s way out of line as a way of dis-regarding it when you interpret your chart. Over time, you’ll know more about how your chart usually looks, and it will be easier to know for sure if an off number really is a fluke. Noting anything out of the ordinary going on in your life can also help you explain a fluke high temperature (see the box on page 50).
Understanding Your Chart
A chart ignoring an unusually high temperature.
Looking at a chart filled in through one entire
cycle, here’s what you can expect to see. Estrogen predominates among your
hormones during the first part of your cycle, and it turns down the thermostat
a bit when it is in charge. In this follicular phase, BBT is generally between
97°F and 97.5°F and should be pretty stable. In the average twenty-eight-day
cycle, this first phase—from when your period starts until you ovulate—usually
lasts fourteen days, but it can last as few as twelve or as many as fifteen
days.
A chart highlighting the temperature dip when
there is a surge in LH.
Then
progesterone takes the wheel, and it warms things up a bit. When you ovulate,
your temperature will go up within twenty-four hours to at least 0.4°F higher than
the highest temperature over the previous six days. Your temperature will
generally stay up for twelve to sixteen days—the average luteal phase BBT is
between 97.6°F and 98.6° F—until your period begins again. If you get pregnant,
your temperature will remain elevated for more than eighteen days, as
progesterone stays on as boss during implantation and gestation.
Some
women get a temperature drop when LH surges just before they ovulate. If you
are one of them, you can watch for this drop in your chart and take it as a
sign to have sex if trying to conceive. Not everyone gets this dip, but women
who do usually get it every month, and it will be obvious on your chart (see
the sample chart showing this dip).
Other
than that, you want to watch for the upward temperature shift so that you can
be sure you are ovulating. Also pay attention to the length of the luteal
phase. If it is too short, you may conceive but then have problems with
implantation. (See page 200 for more on luteal phase defect, or LPD.) And, of
course, once you are familiar with your body’s patterns, the chart can help you
predict when you will ovulate, and you can time intercourse accordingly. Just
keep in mind that the chart alone won’t tell you for sure that you are
ovulating until it is too late to conceive in that cycle.
What to Watch For on Your Chart
A few common BBT chart patterns can indicate fertility trouble. If you spot one of these on your chart, bring it to your doctor’s attention.
PHASE 1 (MENSTRUATION)
BBT that stays high for one or two days after the start of your period
BBT that stays high for one or two days after the start of your period
PHASE 2 (PRE-OVULATION)
BBT that doesn’t stay steady around 97°F to 97.5°F• BBT above 97.8°F (spikes in temperature can impair egg development and make you ovulate early)• Consistently low BBT• Follicular phase less than ten days/early ovulation (the uterine lining may not be thick enough for implantation)• Follicular phase longer than twenty days (estrogen is building up too slowly; the resulting deterioration in egg quality means an increased risk of chromosomal abnormalities, which increase the risk of miscarriage)
BBT that doesn’t stay steady around 97°F to 97.5°F• BBT above 97.8°F (spikes in temperature can impair egg development and make you ovulate early)• Consistently low BBT• Follicular phase less than ten days/early ovulation (the uterine lining may not be thick enough for implantation)• Follicular phase longer than twenty days (estrogen is building up too slowly; the resulting deterioration in egg quality means an increased risk of chromosomal abnormalities, which increase the risk of miscarriage)
PHASE 3 (OVULATION)
No spike in BBT to herald ovulation
No spike in BBT to herald ovulation
PHASE 4 (POTENTIAL
IMPLANTATION)
BBT climbs, then sinks, then climbs again, making a saddle shape pattern (low progesterone)• BBT drops erratically, or drops three to five days before period begins (possible luteal phase defect [LPD]) Am I Pregnant?
BBT climbs, then sinks, then climbs again, making a saddle shape pattern (low progesterone)• BBT drops erratically, or drops three to five days before period begins (possible luteal phase defect [LPD]) Am I Pregnant?
A BBT chart can help you tell when you are pregnant. This might not be necessary in this age of easy at-home pregnancy tests, but it’s cheaper than buying a large supply of those pee sticks, handy though they may be. And it’s just cool to understand your body’s rhythms enough to interpret them this way.
A chart showing a triphasic pattern that
indicates pregnancy.
Why Is My BBT Off?
Several common occurrences or
practices can throw off your BBT. To get the most accurate chart, avoid the
ones you can (no electric blankets) or make a note on the chart so you’ll have
a clue about why an unusual temperature might have occurred. The first three
are the most common things that affect BBT.
• Having a fever
• Drinking alcohol
•
Getting less than three hours of sleep or having disturbed sleep
• Taking your
temperature at a different time
• Using a hot pack or electric blanket
•
Breathing through your mouth while asleep or being congested (causing mouth
breathing)
• Traveling to a different time zone
• Taking an anti-inflammatory or
a sleep aid
• Stress
Case Study: Joanne
Joanne didn’t really know when
she ovulated. Her periods were always irregular, she didn’t get the cramping
that some women do, and she’d never thought much about her cervical mucus, much
less the position of her cervix or her BBT.
She always knew when her period was
coming, she told me (Jill), because she experienced PMS symptoms such as breast
tenderness, fatigue, and irritability, but those signals weren’t very helpful in
trying to get pregnant. For months, she’d been squeezing appointments for
unprotected sex with her husband into her hectic schedule, to no avail. I
explained how to keep a BBT chart, which she agreed to do. At her next
appointment, one thing jumped off the chart for me: her temperature dipped just
before she ovulated (when her LH surged). But it did not rise again for several
days, when it should have shot up right at ovulation. She was ovulating, but it
was taking longer than usual.
This slow transition revealed that her body
couldn’t make hormonal shifts smoothly. At ovulation, her body was not
responding efficiently to the rise in progesterone. She could blame the same
problem for those PMS symptoms, though they were occurring as her progesterone
fell. I prescribed herbs meant to ease these hormonal transitions and persuaded
her to fit acupuncture into her busy schedule.
We knew we were getting
somewhere as her PMS symptoms eased and her cycle got more regular. Her BBT
chart kept showing the temperature drop at the LH surge, but now it was
promptly followed by an appropriate rise, signaling ovulation. After six months
of treatment, Joanne conceived and went on to have a baby girl.
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