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

Implantation Dips, Triphasic Patterns and Luteal Length

A woman in bed looking at a thermometer, wondering if your BBT chart can tell her if she is pregnant
There is a way to know if you're pregnant with a BBT chart, but you'll still need to wait until you can take a pregnancy test to know for sure. Michael H / Photodisc / Getty Images

If you chart your basal body temperature, you have likely wondered whether your BBT chart can tell you if you're pregnant before you take a pregnancy test.

Many women read into every little temperature fluctuation. It's just part of the two-week wait obsession and the never-ending search for 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 temperature increase 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 sure, if you reach 18 days past ovulation, and you still don’t have your period, chances are very good that you are pregnant.

Not many women can wait that long without taking a pregnancy test. Still, it is the strongest early sign of pregnancy detectable with a BBT chart.


Mayo Clinic. Basal body temperature for natural family planning.

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