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Triphasic Pattern and Pregnancy


Triphasic Pattern and Pregnancy: a Statistical Analysis

When charting for pregnancy achievement, there is great interest in identifying early signs which may indicate whether or not there is an increased probability of pregnancy in a given cycle. There has been speculation and much anecdotal evidence to suggest a relationship between a triphasic chart pattern and an increased probability of pregnancy, but until now, no large-scale statistical analysis has been done to determine whether or not this is the case.

Our main goal for this study is to determine whether or not a triphasic pattern occurs more frequently on pregnancy charts than on non-pregnancy charts.

Definition of Triphasic Pattern:
For the purpose of this study, a triphasic pattern is defined as a sustained "third level" of higher temperatures beginning at least seven days after the ovulation rise. We used the pattern here exactly as identified by Fertility Friend's charting software. In the rest of this article we will refer to the triphasic pattern in the context mentioned here. Other ways of identifying the pattern may lead to different results. The advantage of our system is that it is an automated procedure and is not subject to human appreciation and its unavoidable bias.

Triphasic Illustration:
For illustration purposes, see the triphasic chart below:

Sample Triphasic Chart

We considered a batch of the most recent charts analyzed on the web site. 149,781 recent charts were considered.

For each chart considered we took note of the following:

We did not consider any chart for which no intercourse during the fertile window was recorded. In other words, all charts considered had a chance to result in pregnancy.

We measured the frequency of the occurrence of the triphasic pattern in our sample for both pregnancy charts and charts not leading to a pregnancy.


Frequency of a Triphasic Pattern for pregnancy charts:


Frequency of a Triphasic Pattern for non-pregnant charts:


Average Days Past Ovulation (DPO) when this pattern occurs:


The results show that the triphasic pattern indeed occurs more frequently on pregnancy charts. Especially interesting are the following results:

  1. The magnitude of the difference is quite significant. This pattern is 179% more frequent on pregnancy charts.

  2. The moment in the cycle at which this pattern is the most likely to occur is nine days past ovulation. This is within the window of the most likely time for implantation. (Wilcox, A. J., D. D. Baird, et al.1999).

  3. Although the pattern occurs with greater frequency on pregnancy charts, most pregnancy charts do not show this pattern. While it is a good sign when you are hoping for pregnancy, you do not need this pattern to be pregnant.

  4. Seeing this pattern does not guarantee or confirm pregnancy. While the probability of pregnancy is increased significantly when you see this pattern, it also occurs on non-pregnant charts and so cannot confirm pregnancy before a pregnancy test can be reliably taken.

What exactly causes this pattern to occur more frequently on pregnancy charts is not definitively known. The most likely possibility is that increased progesterone in pregnancy cycles plays a role in causing this pattern. This is because progesterone raises temperatures and progesterone levels have been found to be higher in pregnancy cycles than in non-pregnancy cycles (Baird, D. D., C. R. Weinberg, et al. 2003). As the pattern occurs around implantation time, there may also be some relationship between this pattern and the production of the pregnancy hormone, hCG, which begins to be produced at this time, or the related rescue of the corpus luteum, which also happens at this time in pregnancy cycles (Baird, D. D., C. R. Weinberg, et al. 2003). Instead of regressing as it does in non-conception cycles, the corpus luteum is "rescued" at implantation time and continues to produce progesterone, often at elevated levels, during early pregnancy in conception cycles (Baird, D. D., C. R. Weinberg, et al. 2003).

Although these results confirm that the triphasic pattern is indeed a possible early pregnancy sign it also shows that it is not an absolute sign either as the pattern also appears on non-pregnant charts. In practical terms this means that seeing this pattern on your chart is indeed a good sign but it is not an assurance that you will be pregnant. Not seeing the pattern on your chart is likewise not an indication that you are not pregnant. It is also important to recognize that there are a variety of other factors that may influence the probability of pregnancy in any cycle. As usual we recommend that you follow the pregnancy test recommendation given by the Fertility Friend pregnancy monitor.

Baird, D. D., C. R. Weinberg, et al. (2003). "Rescue of the corpus luteum in human pregnancy." Biol Reprod 68(2): 448-56.

Wilcox, A. J., D. D. Baird, et al. (1999). "Time of implantation of the conceptus and loss of pregnancy." N Engl J Med 340(23): 1796-9.

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