Just found this that I quoted my earlier percentages from (they were wrong of course!)
Is a Triphasic Chart a Reliable Early Pregnancy Sign?
FertilityFriend.com, a free fertility charting online software company, did an informal analysis of the BBT charts on their site, to see if a triphasic pattern might indicate pregnancy. This was by no means a scientific study, but the results are still interesting to consider.
In their informal analysis, they considered a triphasic pattern to be a second, significant upward shift in temperature of at least 0.3 F, occurring at least 7 days after ovulation.
After analyzing almost 150,000 BBT charts, they found that 12% of all pregnancy charts showed a triphasic pattern. When looking at non-pregnancy charts, they found that only 5% of charts showed a triphasic pattern. So, based on this data, you have about three times more of a chance of being pregnant with a triphastic chart, than without.
The Bottom Line
Having a triphasic pattern on your BBT chart does not guarantee that you’re pregnant, but it does seem to be a good sign. However, it’s important to remember that some women show triphasic charts and are not pregnant. I have a friend whose BBT chart shows a triphasic pattern quite often, and she has not gotten pregnant.
It’s also important to remember that the greater majority of BBT charts do not show a triphasic pattern. So if you don’t see this third temperature shift on your BBT chart, you shouldn’t take that as a sign that you’re not pregnant.
