What is the implantation window?

Written by: Dr. Amy Beckley, PhD, Founder and Inventor of the Proov test the first and only FDA-cleared test to confirm successful ovulation at home.

Written on 8/20/21

what is the implantation window?

Keep reading to learn more about the implantation window and why it’s so important.

Knowing the parts of your cycle is critical to better understanding your reproductive health, especially when you’re trying to conceive. But the truth is that there are many different phases, parts, and events within just one cycle!

Today we’re going to break down an important part of your cycle: the implantation window. Keep reading to learn more about what the implantation window is and why it’s so important.

What is the implantation window and when does it happen?

While getting pregnant can be a complex process, the basic needs are simple: a healthy egg, a healthy sperm, and for them to meet. This is why tracking your cycle so that you can properly identify the fertile window is so important.

As you probably know, the fertile window is when the sperm can actually fertilize the egg (i.e. when conception can occur). Once fertilization occurs and the embryo travels down the fallopian tube, there is another important piece of the pregnancy puzzle: a healthy uterus.

Your uterine lining has been preparing to welcome an embryo since the beginning of your cycle. During the first half of your cycle — the follicular phase — the growing follicles produce estrogen, which thickens your uterine lining.

Then, during the second half of your cycle (also called the luteal phase), progesterone stabilizes the already thick uterine lining and makes it “sticky” enough to allow the embryo to actually implant. Essentially, progesterone makes the uterine lining receptive to an embryo.

The uterine lining is only receptive to the embryo for a very short period of time during the luteal phase. This period of time is referred to as the “implantation window.”

The implantation window opens roughly 6 days after the release of the egg and lasts for 4 days, with the most common implantation day being 9 days past ovulation. It’s important to note that progesterone must remain adequately elevated throughout the entire implantation window in order for successful implantation to occur.

what is the implantation window?

Note that progesterone must remain adequately elevated throughout the entire implantation window in order for successful implantation to occur.

Why is implantation important?

Implantation is important because it marks the first contact between the embryo and the mother; it is the beginning of pregnancy. Without successful implantation, the fertilized egg cannot survive and will disintegrate.

When the conditions are not properly met — meaning the uterine lining isn’t receptive to the embryo or the embryo is not healthy — implantation may occur but be incomplete. This can result in a chemical pregnancy or early miscarriage.

It is estimated that 25-40% of pregnancies end in early pregnancy loss. This means that at least 1 in 4 pregnancies tragically ends in early miscarriage. Of these early pregnancy losses, studies show that 75% are caused by a failure of implantation.

Ensuring a healthy implantation window and adequate progesterone production during this window is essential for giving yourself the best possible chance at a successful implantation and pregnancy — but more on this later!

How do I know when implantation is happening?

While we know when implantation should occur, there really is no way to know exactly when an embryo is implanting in your uterine lining. However, there are a few signs you can look out for.

Implantation spotting

Implantation spotting may be one of the signs that implantation is happening. Most women do not experience it, but when it occurs implantation spotting is usually beige, pink or light brown in color and only lasts for a couple of days.

Implantation spotting occurs when small blood vessels burst as the embryo attaches itself to the uterine lining. But again, it’s pretty uncommon.

It’s typically so light that it may not even be visible unless you wipe. It should not be deep red, abundant, have clots, or be accompanied by pain. If you experience these symptoms after your spotting, they may be caused by the arrival of your period. If you have concerns about spotting or bleeding, we recommend consulting your doctor.


Cramping may be another implantation symptom. Many women report light lower abdominal pain during their mid luteal phase. While elevated progesterone levels may also cause some cramping, implantation is thought to trigger mild discomfort in some women.

One thing to note is that implantation cramps are typically so light and short that they get overlooked. If you are experiencing real pain during the luteal phase, this may be a sign of other underlying health issues in which case we recommend consulting your doctor.

Basal body temperature shift

A shift in your basal body temperature (BBT) is another way to confirm implantation has occurred. Your BBT is your body’s lower resting temperature and many women track BBT in order to predict and confirm ovulation.

Around implantation, some women may experience an “implantation dip,” which is a decrease in BBT for no longer than one day. It usually occurs about 7 to 8 days after suspected ovulation, around when implantation should occur.

BBT, however, can be easily influenced by many external factors, including: room temperature, alcohol consumption, or snuggles from a loved one or furry friend. These can cause decreases in BBT that some women may take as an implantation dip.

A positive pregnancy test

The clearest sign implantation occurred is without a doubt a positive pregnancy test. Once it starts burrowing in the uterine lining, the embryo starts to produce hCG, the pregnancy hormone.

HCG is first detectable in blood and a day or two later it will also show up in your urine. Some home pregnancy tests claim they are able to detect pregnancy as early as 6 days before your next suspected period. For a luteal phase of 14 days, that would mean hCG would show up in urine around 8 days past ovulation.

However, the science shows us that implantation most commonly occurs on days 8, 9, and 10 past ovulation. Since it takes a few days for hCG to show up in your urine, the earliest you could get a positive pregnancy test if your embryo implanted on day 8 past ovulation would be day 10.

This means testing too early could cause unnecessary stress and disappointment. Waiting to test for pregnancy until after a missed period may provide more accurate results.

what is the implantation window?

Since it takes a few days for hCG to show up in your urine, the earliest you could get a positive pregnancy test if your embryo implanted on day 8 past ovulation would be day 10.

How can I support implantation?

In order for successful implantation to occur we need a healthy embryo and a receptive uterine lining. While it may seem like these two things are out of our control, confirming successful ovulation and improving progesterone levels can help ensure your uterine lining is “sticky” enough for that embryo.

Successful ovulation refers to an ovulatory event in which PdG (a urine marker of progesterone) levels remain elevated for long enough to allow for the best possible chance at conception. In fact, studies show that elevated PdG levels during days 7-10 past peak fertility (i.e. a positive ovulation test) increases the chances of successful pregnancy from just 19% all the way to 92%.

Proov Confirm is the first and only FDA cleared PdG test kit to confirm successful ovulation at home. With Proov Confirm, you can non-invasively monitor your PdG levels during the critical 7-10 days past peak fertility window to ensure your PdG levels are elevated for long enough to allow for implantation and conception.

The implantation window may seem like a mystery but the more you know about implantation and your PdG levels, the better set up you’ll be for success!

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“Hormone balance plays a huge role in fertility, and understanding what’s going on with your hormones doesn’t have to be such a mystery.

It’s actually way easier than most people realize.” 

— Amy Beckley, Proov Founder