Understanding the Implantation Dip on Body Basal Temperature Charts

Brief Temperature Drop as a Pregnancy Indication

Basal body temperature chart with ovulation and implantation dip
Rachel Gurevich

An implantation dip is a one-day drop in your basal body temperature?(BBT) that occurs during the luteal phase of the menstrual cycle (about seven?to 10 days after ovulation). While anecdotal evidence has suggested that the drop is seen more often on pregnancy charts than it is on non-pregnancy charts, an implantation dip is not a guarantee that you’re pregnant.

Here’s how to recognize an implantation dip on your BBT chart, what causes it, and what the actual odds are that you're pregnant if you see one.

What Is an Implantation Dip?

If you’re looking up information on implantation dips, then you likely already know the basics of basal body temperature charting. If you don't know or need a refresher, here is a brief review of how basal body temperature charting works.

Your basal body temperature, or BBT, is your body’s temperature at rest. It responds to changes in your internal and external environment.??

Factors that can affect your BBT include:

  • The amount and quality of your sleep (including changes to your wake-up time)
  • Temperature changes in your environment (both outside and in your home, especially your bedroom)
  • Whether you are using hormonal birth control
  • Whether you have a fever (and if so, whether you are taking medication to reduce your fever)
  • Whether you’re fighting an illness or infection
  • Whether you've consumed alcohol
  • Your stress levels (physical and emotional)
  • Your hormone levels

To understand implantation dips, you need to know how hormones affect your basal body temperature. After you ovulate, it will be a few tenths of a degree higher. The jump in temperature is caused by the hormone progesterone, which increases after ovulation.??

An implantation dip is a one-day drop in temperature on a basal body temperature chart. It occurs about one?week after ovulation.

Usually, a dropping temperature is a sign that?your period is coming?or has already arrived. Your period should not arrive seven to 10 days after ovulation, which means that you wouldn’t expect a temperature drop at this time.

With an implantation dip, the fall only lasts a day—your temperature will go back up the next day. This is unlike what happens after your period starts, in which case your temperature drops and stays down.

The dip can be slightly lower than the rest of your post-ovulation temperatures, or it may drop below the coverline on your fertility chart.??

Coverline

The coverline is an imaginary horizontal line on your BBT chart that separates average temperatures before ovulation from average temperatures after ovulation.

The dip appears?during the luteal phase of your cycle—the time between ovulation and your expected period. Implantation of an embryo usually occurs between days seven?and 11 of the luteal phase.?? Therefore, some people attribute a sudden one-day dip in temperature to implantation.

What Causes an Implantation Dip?

Despite its name, it's not clear if embryo implantation causes a temporary drop in basal body temperature. Non-pregnancy charts can also have the dip, which would mean that the phenomenon is not exclusive to pregnancy.

One theory is that the hormone estrogen causes the dip. Estrogen peaks twice during your cycle. The first (and biggest) surge occurs just before ovulation and leads to fertile cervical mucus and a boost in sexual desire.??

There is a second surge about midway through the luteal phase (after ovulation and before your next expected period). This surge isn’t as high as the first, but it is still significant.

The hormone progesterone raises your body temperature, while estrogen has a counter effect (it lowers your temperature).?? The second surge in estrogen could be why some women experience implantation dips.

Estrogen levels are also higher in women who are pregnant.?? This fact could explain why a temperature decline is seen more frequently on pregnancy charts. However, even non-pregnant women get the secondary estrogen surge during the luteal phase, which is why the dip also appears on non-pregnancy charts.

Some women also notice a dip the day before they ovulate, which is likely caused by the primary estrogen surge that comes just before ovulation.

Does an Implantation Dip Mean You're Pregnant?

A?free fertility charting?app called Fertility Friend did an informal analysis of its users' BBT charts to see if an implantation dip could indicate pregnancy.??

While the statistical analysis of just over 100,000 BBT charts doesn't qualify as a scientific study, the results were still interesting. The analysis reviewed the charts of both pregnant and non-pregnant women looking for:

  • Charts that detected ovulation
  • Dips in temperature of at least 0.3 F occurring after ovulation
  • The drop showing up between days five?and 12 of the luteal phase

On non-pregnancy charts that detected ovulation, 11% had an implantation dip. On the other hand, 23% of pregnancy-positive charts had an implantation dip. Looking at their statistics, twice as many of the pregnancy charts showed an implantation dip.

Approximately 75% of pregnancy BBT charts did not have a dip—which means that if your chart doesn't have a dip, you can't draw a conclusion about whether or not you could be pregnant.

In the informal chart analysis, most women who were pregnant didn't get a dip; the dip more often appeared on non-pregnancy charts.

While you're more likely to see a one-day temperature drop if you're pregnant, it's not a definitive sign of being pregnant. You might see a small dip on your chart almost every month on the seventh or eighth day after you ovulate.

A Word From Verywell

Seeing an implantation dip on your BBT chart is more likely when you are pregnant, but it is not a reliable sign of pregnancy. Your basal body temperature chart can't tell you with any degree of certainty if you're pregnant—you'll need to take a pregnancy test to know for sure.

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