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What Happens During a Menstrual Period?

Updated on August 23, 2014

I frequently get asked if it's possible to have a period while you're pregnant, which is what has prompted me to write this article. In particular, a recent naysayer has been coming onto my early pregnancy symptoms article in an effort to discredit me for saying that you cannot have a period while you are pregnant. Though I've deleted these comments, this person keeps coming back, and I thought it might be best if I went ahead and addressed the issue of what happens during a period so that my readers will have an opportunity to understand that it is biologically impossible to have a cycle during pregnancy except in the very rare case of a double uterus, which is addressed below.

This article attempts to address why it's impossible to have a menstrual cycle or a period during pregnancy. Bleeding during pregnancy is common, and is not always abnormal. Readers are asked to read in order to understand that not all vaginal bleeding is a "menstrual period" and for more information about how the cycle works, including the reasons that it's biologically impossible to have a period and continue to be pregnant unless you have a double uterus.

I am not a medical professional. If you have questions about your menstrual cycles, please contact your doctor for advice!

Knowing how your period works will help in understanding why you can't have a period when you're pregnant -- except in very rare cases.
Knowing how your period works will help in understanding why you can't have a period when you're pregnant -- except in very rare cases. | Source

Why You Need to Know Your Body

I believe that every woman needs to know how her cycles work. Not only will understanding your body and your cycles help you to become pregnant when you are ready, but it will help you to understand your body's reactions to various symptoms. Because I write about pregnancy, and specifically about the early symptoms of pregnancy, many women ask me whether their symptoms indicate that they are pregnant, or indicate that their period is about to come.

The key is to know your body and to know the common symptoms of pregnancy, the common symptoms of the onset of your menstrual period, and how alike these symptoms sometimes are. I have written, and will continue to write, about the symptoms of various women's health issues, but I feel that this is the most important topic that I can cover for the women who read my articles.

Many women don't know what happens during their period, and this creates confusion for those who have had a period, but continue to have symptoms of pregnancy.

So, we'll start by talking about your reproductive system.

Were you taught about your menstrual cycle in health class?

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The Female Reproductive System

The female reproductive system consists of four main parts: The ovaries, the Fallopian Tubes, the uterus, and the vagina. You probably learned something about this system in high school health class, but in most cases, the class doesn't go far enough to fully define what happens during your menstrual cycle.

During your menstrual cycle, these five parts work together to allow for reproduction to take place.

Your cycle begins with your period (involving the uterus and vagina). The menstrual period is explained below.

The second phase of your menstrual cycle is the follicular phase. This phase of your cycle involves the ovarian follicles. These are the most basic units of the female reproductive system. Each follicle contains a single egg. During the follicular phase, the ovarian follicle develops in preparation to release an egg into the Fallopian tube. Most of the time, your body develops only one ovarian follicle and releases a single egg. Sometimes more than one follicle develops and more than one egg is released into the Fallopian tubes. This may result in fraternal twins.

Your Fallopian tubes connect your ovaries to the uterus. When you become pregnant, an egg is fertilized in the Fallopian tube, and then travels down the tube into the uterus.

The uterus is where an embryo develops into a fetus, and where the fetus develops in preparation for birth. It is the lining of the uterus which is shed during the menstrual period. In some rare cases, a woman may have a double uterus. This lining is flushed from the body via the vagina, which is also the passage through which an infant passes on its way to being born. This part of the reproductive system is also known as the "birth canal."

The uterus is an iconic symbol of womanhood.
The uterus is an iconic symbol of womanhood. | Source

Spotting is common during pregnacy. Periods are not!

Your period is the first phase in your menstrual cycle.
Your period is the first phase in your menstrual cycle. | Source

So What Is a "Period?"

Since the purpose of this article is to explain the menstrual period, I won't dwell on the other parts of the cycle. The purpose of this article is, instead, to explain why it is impossible for a woman with a single uterus to have a period during pregnancy. If you have questions about this, you are welcome to leave your comments at the bottom of this article, but you are asked first to please read through the article thoroughly and with an understanding of the science and biology behind the statement that you cannot have a period if you are pregnant.

The menstrual period is the first phase of your menstrual cycle. It is the phase during which your body cleans out everything it accumulated during the previous phases of the cycle, so that the cycle can repeat itself again.

If you watch the video below, you will see that during the follicular phase (immediately following your menstrual period), your body prepares for pregnancy. The lining of the uterus thickens, and the egg is released at ovulation. If this egg is fertilized by a sperm cell, the newly formed embryo will implant on the wall of the uterus, resulting in pregnancy.

Because your period flushes the egg and the lining of the uterus, you cannot have a period while you're pregnant. The embryo would be flushed with the uterine lining.

Causes of Bleeding During Pregnancy

Normal Bleeding
Abnormal Bleeding
implantation of the embryo on the uterine lining
cevical changes
ectopic pregnancy
doing the baby dance
molar pregnancy

Your period is never a reason you're bleeding during pregnancy!

But I Have Friends Who Had Periods While Pregnant!

I was recently informed of the condition known as "double uterus," (see link to Mayo clinic, above) but I have yet to find any evidence that it is possible to continue to have periods from one uterus while pregnant in the other.

Because I cannot find any information whatsoever about whether it is possible to be pregnant in one uterus and continue to have a cycle in the other, won't speak to this subject.

Why Science Beats Anecdotal Evidence

The science of menstruation indicates (clearly) that it isn't possible for a woman with a single uterus to continue to have a period while she is pregnant, and it is clearly impossible for a women to have her menstrual cycle while she is pregnant.

Unfortunately, many women continue to cite anecdotal evidence in order to support their standpoint that a woman can be pregnant and continue to have a period.

The problem with anecdotal evidence is twofold: One, people lie. Imagine that you are a woman who found out, late in pregnancy, that she was pregnant, and people placed pressure on you for not knowing that you were already pregnant, and therefore being seen by a doctor. You might choose to tell your friends and/or family that you continued to have periods while you were pregnant, and therefore didn't know that you should test.

Another reason is that the average woman doesn't have sufficient information about the reasons for bleeding during pregnancy and therefore assumes that when she sees blood, that it's her period. While it's possible for a woman to bleed monthly during pregnancy (most likely due to cervical changes), this is not the same thing as having a period.

Before Commenting

I note that I have received several comments on my early pregnancy symptoms article attempting to discredit me for saying that it is impossible to have a period while you're pregnant. The people making the comments here and on Facebook cite anecdotal evidence of "several friends" who have had periods during their pregnancies.

Please read the reference articles and watch the videos before commenting to state that it's possible to have a period while you're pregnant. It simply is not.


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