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When does implantation bleeding occur?

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 7/6/21

when does implantation bleeding occur

Implantation bleeding can easily be confused with the beginning of your period or something else.

Implantation bleeding is an early pregnancy symptom that many women look out for. However, implantation bleeding can be easily confused with the beginning of your period or something else. Keep reading to learn more about implantation bleeding, including when it should occur.

What is implantation and when does it occur?

While we may have been taught that getting pregnant is as simple as “egg meets sperm,” it’s actually an extremely intricate process that may require resources and great timing. Many couples start with the timing part of conception — having intercourse when the woman is most fertile. However, there’s another step in getting pregnant that many couples overlook: implantation.

After sperm meets egg and fertilization takes place, the newly formed embryo needs to find a place to implant in the uterine lining, which has been preparing to receive the embryo since the beginning of the cycle. A woman’s uterus is receptive to the embryo for a period of about 4 days during the mid-luteal phase (the second half of your cycle). This period is called “the implantation window.”

Even though implantation is known to occur as early as day 6 past ovulation and as late as day 12 past ovulation, studies show the implantation window most commonly occurs during days 7 to 10 past ovulation, with day 9 being the most common implantation day. Implantation can only be successful if the uterine lining is receptive and the embryo is healthy.

The preparation of the uterine lining starts during the follicular phase (the first half of your cycle). As the follicles are growing and maturing they produce estrogen, one of the to main female sex hormones. Estrogen helps thicken the uterine lining.

Once ovulation occurs, the empty follicle (also called the corpus luteum) starts producing progesterone, the other main female sex hormone. Progesterone’s job is to stabilize the already thickened uterine lining and make it “sticky” enough in order for an embryo to implant.

The uterine lining needs progesterone’s support to stay receptive long enough for a woman to get pregnant. Because of this, progesterone needs to rise and remain elevated during the implantation window to allow for the best possible chance at pregnancy. If progesterone doesn’t reach an optimal level or drops too soon, it can be more difficult for conception to occur.

In fact, progesterone is so important that a recent study found that women who had optimal levels of a progesterone metabolite in their urine during the implantation window had a 92% chance of a successful pregnancy, compared to only a 19% chance for women who did not have optimal levels. The study measured PdG — a urine metabolite of progesterone.

when does implantation bleeding occur

A recent study found that women who had optimal levels of a progesterone metabolite in their urine had a 92% chance of a successful pregnancy, compared to only a 19% chance for women who did not have optimal levels.

What is implantation bleeding?

Some women may notice a bit of a bloody discharge around the day implantation should occur. This is referred to as “implantation bleeding” and often looks more like spotting. It can be pink, light brown, or beige, sometimes with a bit of red.

Only 25% of women have reported implantation bleeding. For some women it may be so light that they mistake it for normal discharge and dismiss it. For others, especially those with irregular cycles, it may be mistaken for an early period.

Some fertility myths say women who experience implantation bleeding have a stronger implantation, however there is no science to back this up. What actually happens during implantation bleeding is when the embryo tries to implant into the uterine wall it can cause small blood vessels to burst. This in turn can cause a tiny amount of bleeding which, mixed with typical vaginal discharge, may appear as light spotting.

How long does implantation bleeding last?

If you are experiencing implantation bleeding, it typically won’t last more than a couple of days. It also shouldn’t get heavier or have any clots.

If your mid-luteal spotting gets heavier or turns into real bleeding, then it’s most likely not implantation bleeding. Tracking your cycle and keeping track of your symptoms is extremely important so that you are able to tell the difference between potential implantation spotting, your period, an ectopic pregnancy, or early miscarriage. If you have concerns about any bleeding (especially if you’ve gotten a positive pregnancy test), we recommend consulting your doctor.

You may also want to keep in mind that spotting before your period usually occurs around the same time in your cycle at implantation bleeding would. Spotting before a period is not necessarily related to a potential pregnancy and may be a sign of low progesterone.

If you are expecting pre-period spotting you might want to have your progesterone or PdG levels tested, especially if you are trying to conceive. Progesterone levels dropping too fast may actually impact implantation, as the lining starts to shed too early and doesn’t allow for implantation to take place.

when does implantation bleeding occur

If you are experiencing implantation bleeding, it typically won’t last more than a couple of days.

What are other symptoms of implantation?

The only way to confirm if spotting was actually caused by implantation is a positive pregnancy test. Yet it’s important to understand that you likely will not get a positive pregnancy test right when implantation spotting starts.

Once implantation occurs, your body starts producing hCG, the pregnancy hormone. It can take a while for hCG to show up in blood and even longer for it to appear in urine, so testing too early could provide inaccurate results. Most home pregnancy tests recommend waiting to test until after a missed period to get the most accurate results.

Some, but not all, women may be able to spot very early signs of pregnancy, such as the following:

  • Implantation cramping is a mild discomfort in the lower abdominal area that some women report around the day of implantation. There is no scientific data supporting a connection between implantation and cramping, but high levels of progesterone are known to cause cramping and for successful implantation progesterone should be elevated. 
  • Tender breasts may be a symptom of very early pregnancy but again, elevated progesterone during the luteal phase may also cause your breasts to be sore. This is a symptom of both early pregnancy and premenstrual symptoms, so it can be easily mistaken for something it’s not.
  • Nausea is one of the most common early pregnancy symptoms. However, it’s pretty rare to notice it before getting a positive pregnancy test, so if it happens before your BFP it’s likely not related to pregnancy.
  • Fatigue may be a sign of pregnancy but can also be a sign of high progesterone levels.
  • Mood swings are common in early pregnancy, also caused by changes in progesterone levels, but they are also a common occurrence in the days preceding your period.
  • Some women also report digestive issues, such as bloating, gassiness, or changes in bowel movements as the first sign of pregnancy. This is due to an increase in progesterone, which slows down metabolism through the gut.

Understanding when to expect implantation bleeding can help you if it’s actually implantation bleeding or a sign of something else!