Fertility basics

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

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 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.

What causes spotting during the luteal phase?

Spotting during the luteal phase is a normal feature in some menstrual cycles. Some women spot every cycle, and other women spot only rarely. It’s typically caused by a mid-luteal phase surge in estrogen that causes a brief dip in progesterone.

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.

Spotting can also occur in very early pregnancy, before the 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.

Is spotting a sign of pregnancy?

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 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. The study referenced above found “no support for the hypothesis that implantation can produce vaginal bleeding.”

Lindsay Meisel

Lindsay is Ava's Head of Content. She has over a decade of experience writing about science, technology, and health, with a focus on women's health and the menstrual cycle.

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