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Can You Detect Early Pregnancy with a Body Basal Temperature Chart?

Implantation Dips, Triphasic Patterns, and Luteal Length


Updated May 30, 2014

The woman who measures a thermometer in a bed
Michael H/Photodisc/Getty Images

Many women, including myself, read into every little temperature fluctuation on their body basal temperature (BBT) chart during the two-week wait in search of early pregnancy signs. But is the search worthwhile, or is it just one more thing to make yourself crazy with? Can you actually detect early pregnancy signs by reading into your BBT chart?

The answer is yes -- and no.

Implantation Dips and Triphasic BBT Chart Patterns

Two big things that women look for on a BBT chart are an implantation dip, which is a one-day drop in temperature about a week after ovulation, and a triphasic temperature pattern, which is a second, upward shift in temperature occurring about one week after ovulation.

Both of these BBT patterns are thought to be signs of increasing progesterone and implantation of the embryo. However, neither is a reliable early pregnancy sign.

The majority of the time, an implantation dip is nothing more than a mid-cycle dip in temperature, and does not indicate pregnancy. Seeing a triphasic pattern on your BBT chart is slightly more likely to indicate a potential pregnancy, but it is also no guarantee.

Also, many women who get pregnant get neither an implantation dip nor a triphasic pattern on their BBT chart. So not seeing these signs is no reason to feel disappointed.

Luteal Phase Length as an Early Pregnancy Sign

So how can you use a BBT chart to indicate pregnancy? The old-fashioned method: By waiting to see if your luteal phase -- the time between ovulation and your expected period -- is longer than usual.

For most women, their luteal phase does not vary by more than a day or two from month to month, even if the length of their menstrual cycle does vary. So, for example, a woman’s cycles may vary between being 30 and 35 days, but her luteal phase may consistently be 12 or 13 days long.

If you see that your luteal phase has gone at least one day past the usual length, you might be pregnant. If it goes two days past the longest luteal phase you’ve ever had, the likelihood of being pregnant is even higher. This is a good time to take a pregnancy test.

To be absolutely sure, if you reach 18 days past ovulation, and you still don’t have your period, chances are very good that you are pregnant.

I don’t know many women who can wait that long without taking a pregnancy test! Still, it is the strongest early sign of pregnancy detectable with a BBT chart.

More on how to get pregnant:

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Weschler, T. (2002). Taking Charge of Your Fertility (Revised Edition). United States of America: HarperCollins Publishers Inc.


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