Implantation dip: What it means for pregnancy & BBT chart

BBT during the menstrual cycle

The menstrual cycle is intimately connected to our body temperature. The very same hormones that govern the menstrual cycle also affect body temperature, resulting in a characteristic temperature curve that follows the changing hormone levels during each cycle. By tracking your basal body temperature (BBT), the body’s lowest resting temperature, you can get insights into your cycle — and clues about pregnancy too. To measure your BBT, you need to take your temperature as soon as you wake up in the morning using a special kind of thermometer that measures with two decimal points [1].

So, what can you expect from your temperatures during your cycle? The menstrual cycle consists of two main phases separated by ovulation. The follicular phase, which starts on the first day of your period and continues until ovulation, is characterized by lower temperatures. Estrogen levels start out relatively low at the beginning of this phase and then rise as the body prepares for ovulation — this hormone is known to lower body temperature [2]. After ovulation, the body releases progesterone which causes the body temperature to rise by an average of 0.5-1.0°F (0.3-0.5°C). Temperature will stay elevated throughout the second part of the menstrual cycle, the luteal phase, before dropping again around the time the next period starts [3]. 

What is an implantation dip?

If you’ve spent time in pregnancy planning forums online, you may have seen mentions of a one-day temperature dip of a few tenths of a degree in the luteal phase. This is known as an implantation dip. It’s said to happen roughly between a week and a week and a half after ovulation, and temperatures then return to luteal phase levels again. While some people say that this dip is an early sign of pregnancy, it’s actually not as straightforward as that. 

To this date, there’s no peer-reviewed research about the implantation dip. While some people do seem to experience a one-day temperature dip in the luteal phase, we don’t know for sure how common it is, or even if (or how) it’s related to pregnancy at all. 

One suggested theory behind the implantation dip is that it’s caused by a second estrogen surge in the luteal phase, which could theoretically result in a temporary drop in temperature. There is indeed a surge in estrogen levels that happens mid-way through the luteal phase [4], and estrogen is known to lower body temperature [2]. However, more research is needed and, again, there are no studies specifically about the implantation dip. It’s also worth mentioning that the second estrogen surge happens in all cycles, not only those that result in pregnancy. 

When does implantation happen?

Implantation, when the fertilized egg cell implants in the uterine wall, usually happens around 8-10 days after ovulation [5]. There are some steps preceding it though: during ovulation, one of the ovaries releases an egg, which is fertilized when it meets a sperm cell. The fertilized egg (now called a zygote) starts dividing into more cells while it travels down the fallopian tube. It takes about a week for the clump of roughly 100 cells — which has changed names again by this point and is now called a blastocyst — to reach the uterus where it attaches to the uterine wall [6].

Turning back to the implantation dip, research on the topic is very limited so we don't know if or how it lines up with when implantation actually happens.

Does an implantation dip always happen?

Not everyone who gets pregnant has an implantation dip. To complicate things further, it’s also possible to experience a temperature dip in the luteal phase even when pregnancy doesn’t occur. In short, the implantation dip doesn’t always happen and it’s not clear whether a temperature dip in the luteal phase is linked to implantation in some way or if it happens for another reason. 

What happens after the implantation dip?

If you do see a temperature dip in your chart part-way through the luteal phase, your temperature should increase again and stay elevated afterward. Towards the end of your cycle, you may start experiencing some physical or emotional symptoms — early pregnancy symptoms can be very similar to symptoms of PMS, so it can be hard to tell them apart. If your period doesn’t show up when it usually does, it’s a good time to take a pregnancy test.

What can affect BBT?

So far, we’ve talked about how hormones are linked to temperature, but it’s not just the menstrual cycle that affects it. It’s normal for our body temperature to change a little bit day-to-day without any major reason. However, if you’re tracking your cycle using the basal body temperature method, the following circumstances can affect it:

• Sleeping more or less than usual
• Being sick
• Drinking alcohol
• Recent use of hormonal birth control
• Certain medications
• Some thyroid conditions

[3, 7]

If you’re using Natural Cycles, the NC° algorithm will automatically detect unusual temperatures and exclude them from its calculations, and you also have the option to manually exclude your temperature if you know something was out of the ordinary that night.

Does an implantation dip mean I’m pregnant?

No, a temperature dip in the luteal phase isn’t a sure sign of pregnancy. There are also many things that can affect our temperature, so you may notice a single lower temperature than usual without it being a result of hormonal changes (that’s why it’s important to look at temperature trends over time during your cycle). The only way to be certain is to take a pregnancy test. 

However, even though an implantation dip can’t be trusted as a pregnancy sign, your chart can still give some clues as to whether you may be pregnant. 

What does a pregnancy BBT chart look like?

Due to the higher levels of progesterone, temperatures rise after ovulation and stay high throughout the luteal phase. Progesterone helps the uterus prepare for implantation and supports the development of the fetus in early pregnancy. If conception doesn’t happen, however, the body stops producing progesterone within 14 days, causing progesterone levels to fall as the cycle ends [8]. As a result, the basal body temperature drops when we get our period. 

If conception does happen, the body instead continues to produce progesterone and temperatures will remain high even after the expected period. If your BBT remains high and your period isn’t arriving as expected, it’s a good time to take a pregnancy test. However, it’s good to know that it’s possible to have elevated temperatures past the day of your expected period even if you’re not pregnant [9].

If you’re using Natural Cycles to plan your pregnancy, the app will notify you when it’s time to take a pregnancy test based on your individual cycle — taking into account your ovulation date and your individual luteal phase length — so you don’t have to wonder if it’s too early to test.

Other early pregnancy signs

We know the two-week wait can be stressful, and it’s normal to look for signs that this month is the one. To make things even more difficult, many common PMS symptoms are very similar to those of early pregnancy. In the end, the only sure way to confirm that you’re pregnant is to take a pregnancy test, but there are also some other early pregnancy signs to look out for:

• Late period: Not getting a period as expected is perhaps the most common sign that you may be pregnant.
• Sore breasts: Breast feeling swollen, sore, or tender is common in early pregnancy. 
• Feeling nauseous: Often referred to as “morning sickness”, nausea is a common symptom of pregnancy that typically starts around week 4-6 (around 2-4 weeks after conception) and usually gets better in the second trimester
• Light bleeding: Some may experience a light bleed known as implantation bleeding around the time of expected implantation, and bleeding in the first trimester has been found in 25% of pregnancies [10]. While it’s common, it’s a good idea to speak with your healthcare provider if you experience bleeding during pregnancy.
• Cravings: You may notice that you’re craving different foods than you’re used to.
• Tiredness: It’s common to feel tired in early pregnancy due to the hormonal changes going on in the body. Make sure you’re kind to yourself and listen to your body if you need some extra rest. It’s also a good idea to speak with your healthcare provider if you’re feeling very tired during this time.

[11]

Plan a pregnancy with Natural Cycles

While the implantation dip isn’t a sure way of knowing if you’re pregnant, tracking your body temperature can still give you valuable insights into your menstrual cycle and fertility. That’s where Natural Cycles comes in. NC° Plan Pregnancy lets you know when you’re fertile and have the highest chance of getting pregnant, and it also notifies you when it’s time to take a pregnancy test, all based on your individual cycle data. Measure your BBT with an NC° Thermometer, or wear an Oura Ring or Apple Watch while you sleep, and let our algorithm do the rest. Why not see if Natural Cycles could be right for you?