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Fertility basics

Implantation Bleeding: An Idea Without Scientific Evidence

implantation bleeding

Essential Takeaways

  • While implantation bleeding is a popular concept, there is no evidence that it truly exists
  • The physiological process of implantation does not cause bleeding
  • Studies show that bleeding is more likely to indicate an impending period than an early pregnancy

Implantation bleeding is the name commonly used to describe light pink or brown discharge that occurs in very early pregnancy, before you even get a positive pregnancy test.

This light spotting is considered by many to be a sign that implantation has occurred and an early symptom of pregnancy. It is said to be caused by the egg burrowing into the uterine wall. However, the evidence for this assertion is spotty. More on this below.

How can you tell if spotting is caused by implantation?

Light bleeding or spotting is common during the premenstrual phase (also called the luteal phase) of a woman’s cycle, whether or not she is pregnant. So how can you tell the difference between normal luteal phase spotting and a true implantation symptom? You can’t.

Can implantation cause bleeding?

According to the research, implantation probably does not cause bleeding.

Why? Well, for one thing, when bleeding does occur during early pregnancy, it’s unlikely to occur during the implantation window of 6 – 12 days past ovulation. A 2003 study of 151 pregnant women found that most episodes of bleeding occurred at least 5 days after implantation.

The authors of that study concluded: “We found no support for the hypothesis that implantation can produce vaginal bleeding.”

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Is bleeding a sign of pregnancy?

Bleeding in the days before your period is due should not be considered a positive sign of pregnancy.

According to a 2016 study of 549 women who were trying to conceive, bleeding is more likely to indicate an impending period than pregnancy. The authors of that study concluded:  “Intermenstrual bleeding statistically significantly decreases the odds of conceiving in that cycle.”

How can you tell if it’s implantation bleeding or your period?

Bleeding can occur both during early pregnancy and in the days leading up to your period. When a woman who has premenstrual bleeding goes on to find out she’s pregnant, we often call it implantation bleeding. But this is Monday morning quarterbacking: we decide what to call the bleeding based on whether a woman ends up being pregnant, not based on real evidence that the bleeding was caused by implantation.

According to medical research, when bleeding does occur in early pregnancy, it is probably not caused by implantation.

Bleeding is common in early pregnancy, affecting 10 – 15% of all pregnant women. Most of the time, this bleeding is unexplained. There’s simply no convincing evidence that points to implantation as the cause of this bleeding.

What causes implantation bleeding?

It’s common for bleeding to occur during very early pregnancy, but as described above, there is no evidence that this bleeding is caused by implantation. But something must have caused it, so what was it?

There are several possible alternate explanations for implantation bleeding:

  • Drop in progesterone levels: Progesterone is the hormone that maintains the uterine lining. A drop in progesterone is what causes your period to begin. Progesterone levels can begin to fall a few days before your period is due, and this can lead to light bleeding or spotting before your period. This spotting may occur regularly with every cycle, or only rarely.
  • Unexplained early pregnancy bleeding: Between 10 – 15% of pregnant women experience bleeding during early pregnancy. There isn’t always a clear explanation for this bleeding, but it tends not to occur on the day of implantation (most often it occurs at least 5 days after implantation).
  • Chemical pregnancy: Bleeding or spotting can be a sign of miscarriage. For very early miscarriage—called chemical pregnancy—women may notice bleeding around the time of a missed period.

How long does implantation bleeding last?

Many women report that it is light and short, and lasts only a few days. It occurs around the time of a missed period, or about 10 – 14 days after ovulation.

Of course, you now understand that the bleeding commonly identified as implantation bleeding most likely is caused by something else entirely.

View sources

Vaginal bleeding in very early pregnancy E.W. Harville, A.J. Wilcox, D.D. Baird, C.R. Weinberg. Human Reproduction, Volume 18, Issue 9, September 2003

Natalie M. Crawford, David A. Pritchard, Amy H. Herring, Anne Z. Steiner, Prospective evaluation of the impact of intermenstrual bleeding on natural fertility, Fertility and Sterility, Volume 105, Issue 5, 2016, Pages 1294-1300, ISSN 0015-0282,

Lindsay Meisel

Lindsay Meisel is the Head of Content at Ava. She has over a decade of experience writing about science, technology, and health, with a focus on women's health and the menstrual cycle. Her work has been featured on The Fertility Hour, The Birth Hour, The Breakthrough Journal, and The Rumpus.

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