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How Does BBT Affect Early Pregnancy Detection?

Updated December 16, 2014.

Written or reviewed by a board-certified physician. See's Medical Review Board.

Many women (including myself, I admit) scour their BBT charts for early pregnancy or implantation signs. One of the more commonly looked for implantation signs is an implantation dip. But is an "implantation dip" a real sign of an embryos implantation? Is it a genuine sign of early pregnancy during the two-week wait?

What Is an Implantation Dip?

As you may remember, ovulation can be detected on a basal body temperature chart by a slight shift in temperature mid-cycle.

For more about basal body temperature chart, read this step-by-step piece on how to chart your body basal temperature and how to detect ovulation with a BBT chart.

An implantation dip is a one-day drop in temperature on a basal body temperature chart, occurring about one week after ovulation. The dip appears during the luteal phase, the time between ovulation and your expected period. Implantation of the embryo usually occurs between days 7 and 11 of the luteal phase, and this is why some people attribute this sudden one-day dip in temperature to implantation.

The dip in temperature may just be slightly lower than the rest of the post-ovulation temperatures, or it may even dip below the "cover line" on a fertility chart. (The cover line is an arbitrary line that the temperatures on average were below before ovulation, but appear on average above after ovulation.)

Does an Implantation Dip Mean You Are Pregnant?, a free fertility charting online software company, did an informal analysis of the BBT charts on their site, to see if an implantation dip might indicate pregnancy.

This was by no means a scientific study, but the results are still interesting to consider.

They did a statistical analysis of just over 100,000 BBT charts, of both pregnant and non-pregnant women. They looked for a dip in temperature of at least 0.3 F, occurring between days 5 and 12 of the luteal phase.

They found that on non-pregnancy charts that detected ovulation, 11% had an implantation dip. On the other hand, they found that on pregnancy positive charts that detected ovulation, 23% had an implantation dip.

Looking at their statistics, twice as many of the pregnancy charts showed an implantation dip. However, it's also important to note that of the pregnancy positive charts, approximately 75% did not have the dip. Plus, on charts that were not pregnancy positive, 11% did show the dip.

So while you're more likely to see a dip when you're pregnant, it is not a definitive sign of being pregnant, and not having the dip doesn't mean you're not pregnant.

I actually get a small "dip" on my chart almost every month on day 7 or 8 post-ovulation, and I know other women who also show "implantation dips" on their charts month after month - but they are not pregnant.

The funniest thing about implantation dips? The one month I was charting and did get pregnant, I actually did not show an implantation dip.

The Bottom Line

Having an implantation dip is more likely when you are pregnant, but it is not a reliable sign of pregnancy. Women can have the so-called implantation dip when they are not pregnant, and plenty of women who are pregnant do not show an implantation dip on their BBT chart.

You can still have fun looking for an "implantation dip" - but there's no reason to get your hopes up if you have one, or feel disappointed if you don't.

More on how to get pregnant:

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Is There a Such Thing as an Implantation Dip? Accessed on January 1, 2009.

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