Fertility basics

Implantation Bleeding Isn’t Really a Thing. Here’s Why.

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

If you notice light blood or brown discharge in the days before your period is due, you may wonder if it’s implantation bleeding. This light spotting is considered by many to be an early sign of pregnancy. It occurs during the implantation window (6 – 12 days after ovulation), and is said to be caused by the egg burrowing into the uterine wall.

But since spotting during the luteal phase is so common even when a woman is not pregnant, how do you know the difference between normal luteal phase spotting and a true implantation symptom? The answer is that you can’t, and what’s more, the whole idea of implantation bleeding may be a myth.

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

Calling something implantation bleeding is a bit like Monday morning quarterbacking. If there is spotting in a non-pregnancy cycle, we just call it spotting. But if there’s spotting in a pregnancy cycle, we call it implantation bleeding.

Given the high incidence of light bleeding or spotting in both pregnant and non-pregnant cycles, it’s almost impossible to know whether the spotting has anything to do with implantation. And there is good reason to think that it doesn’t.

Why? Well, for one thing, spotting happens more frequently in cycles when a woman is not pregnant. And when you think about it, this makes a lot of sense. Spotting is usually caused by a drop in progesterone (because progesterone is the hormone that helps maintain the uterine lining).

If implantation has occurred successfully, hCG secretion would help ensure that there was no drop in progesterone levels in the first place. One study on bleeding in early pregnancy found “no support for the hypothesis that implantation can produce vaginal bleeding.”

What causes implantation bleeding?

We know that the phrase “implantation bleeding” is a misnomer. But something must have caused it, so what was it?

By itself, spotting or brown discharge during the luteal phase doesn’t have any conclusive meaning. It can happen when progesterone levels are too low, but it can also happen when progesterone levels are perfectly normal. It can happen when you are pregnant, and it can also happen when you’re not.

Here are several more likely possible explanations for this type of bleeding:

Luteal phase spotting

For some women, it’s normal to occasionally experience spotting during the luteal phase (the second half of your cycle, before your period is due). Some women spot every cycle, and other women spot only rarely. This type of occasional spotting is caused by a mid-luteal phase surge in estrogen that causes a brief dip in progesterone.

Progesterone is the hormone that maintains the uterine lining, so a drop in progesterone levels can cause spotting. This is normal and should not be considered implantation bleeding.

Early pregnancy spotting

While there is no evidence that the process of implantation causes spotting, spotting can occur in very early pregnancy, before or after a missed period.

One study found that early pregnancy spotting occurred for nine percent of women, around the time of their expected period. This spotting was usually not heavy enough to be confused with a period. It also tended not to occur on the day of 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?

If you research accounts of implantation bleeding, you’ll find that 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

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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