Retrograde Menstruation: What Is It and How Is It Connected to Endometriosis?
- Medically Reviewed by Dr. Charles Nagy, MD, FRCOG | SRC Accredited
Every month, something happens inside the pelvis that most women never feel or hear about.
A small amount of menstrual blood, instead of leaving the body through the cervix, travels backwards through the fallopian tubes and settles in the pelvic cavity. It is quiet, common, and usually harmless.
For some women, though, it may be the opening chapter of a much longer story: years of period pain dismissed as normal, heavy bleeding, pain during intimacy, fatigue, and difficulty conceiving.
That story has a name, endometriosis, and the backward flow described above sits at the center of the leading explanation for how it begins.
What is Retrograde Menstruation?
So, what is retrograde menstruation? It is the backward movement of menstrual blood and shed endometrial cells out through the fallopian tubes into the pelvic cavity, rather than downward and out of the body. Endometriosis affects women of reproductive age.
One point matters early: retrograde menstruation is neither a disease nor a diagnosis. Laparoscopy performed during menstruation has found blood in the pelvic fluid of the large majority of women with open fallopian tubes.
Quick snapshot: almost every woman experiences it. Only a few go on to develop endometriosis. The difference lies in what happens next.
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What Does a Retrograde Menstruation Diagram Show?
Search for a retrograde menstruation diagram, and you will see the same illustration: a cross-section of the uterus with two sets of arrows. One point down through the cervix, showing normal flow.
The second curves up and out through the fallopian tubes, spilling into the space around the ovaries, bowel, and bladder.
That single image makes one thing obvious. The pelvic cavity is an open space, so anything that reaches it can settle almost anywhere, which is why endometriosis lesions appear on the ovaries, the pelvic lining, and the bowel.
What Causes Retrograde Menstruation?
Patients often ask what causes retrograde menstruation, expecting a single culprit. In reality, it appears to be a normal by-product of uterine contractions during a period. Several factors can make the backward flow more pronounced:
- Heavy or prolonged periods, which increase the volume of tissue involved.
- Short cycles and more frequent bleeding.
- Early onset of periods, meaning more cycles over a lifetime.
- Obstruction to normal outflow, such as cervical narrowing or a uterine anomaly.
- Abnormal uterine contractions that push the flow in the wrong direction.
None of these guarantees against disease. They simply raise the level of exposure.
Symptoms of Retrograde Menstruation
Here honest information matters. There are no direct symptoms of retrograde menstruation, because the process is silent and cannot be seen on a routine ultrasound. What patients notice are symptoms of what it may lead to:
- Period pain severe enough to interrupt work, study, or sleep.
- Pelvic pain that lingers after bleeding stops.
- Pain during or after intercourse.
- Pain with bowel movements or urination during your period.
- Heavy or clot-filled bleeding.
- Fatigue out of proportion to your activity.
- Difficulty conceiving after 12 months of trying.
If you are searching for symptoms of retrograde menstruation because your periods feel abnormal, the message is simple. The flow is not the thing to investigate. The pain is.
The Retrograde Menstruation Theory Endometriosis
The retrograde menstruation theory endometriosis was first proposed by American gynaecologist Dr John A. Sampson in 1927. Nearly a century later, it remains the most widely recognised explanation for how many cases of endometriosis may develop.
According to this theory, during menstruation:
- Some menstrual blood flows backwards through the fallopian tubes instead of leaving the body.
- This backward flow carries endometrial cells into the pelvic cavity.
- These cells can attach to organs and tissues outside the uterus.
Once implanted, these cells continue to behave as they would inside the uterus. They respond to hormonal changes, thicken, and bleed during each menstrual cycle.
Because this blood has nowhere to drain, it can lead to:
- Chronic inflammation
- Scar tissue (adhesions)
- Pelvic pain and other symptoms associated with endometriosis
However, retrograde menstruation does not explain every case of endometriosis. Studies have shown that many women experience retrograde menstrual flow but never develop the condition.
Researchers now believe that other factors also play an important role, including:
- Genetic predisposition
- Differences in immune system function
- Hormonal influences
- Inflammatory and environmental factors
For this reason, most experts now consider endometriosis to be a multifactorial disease, with retrograde menstruation being one important piece of a much larger puzzle.
References:
Zondervan KT, Becker CM, Missmer SA. Endometriosis. N Engl J Med. 2020.
Vannuccini S, et al. The Main Theories on the Pathogenesis of Endometriosis. 2023. https://pmc.ncbi.nlm.nih.gov/articles/PMC10001466/
How Does Retrograde Menstruation Lead to Endometriosis?
So how does retrograde menstruation lead to endometriosis in some women and not others? Current thinking points to a sequence:
- Endometrial cells reach the pelvic cavity during menstruation.
- In most women, immune cells clear them efficiently.
- In susceptible women, clearance fails, and the cells survive.
- Surviving cells attach, establish a blood supply, and grow.
- Repeated cyclical bleeding drives chronic inflammation and adhesions.
The link between endometriosis retrograde menstruation, and actual disease, therefore, depends less on the flow itself and more on immune function, genetics, and hormone sensitivity. This is why endometriosis often runs in families.
Sampson’s model is powerful but incomplete. It does not fully explain endometriosis in unusual sites, and complementary theories such as coelomic metaplasia and lymphatic spread help fill the gaps.
When to See a Gynecologist for Endometriosis Specialist
Endometriosis is still diagnosed years later than it should be, largely because severe period pain has been normalized for generations.
Seek specialist assessment if pain dictates your calendar, if bleeding is heavy, or if conception is proving difficult.
Accurate diagnosis often requires expert imaging and, where appropriate, diagnostic laparoscopy by a surgeon who routinely treats this condition.
Expert Care for Endometriosis Retrograde Menstruation with Dr. Charles Nagy
With more than 25 years in obstetrics and gynecology across the UK and the Middle East, Dr. Charles Nagy brings a specialist focus to complex gynecological surgery and minimally invasive care.
He holds dual accreditation from the Surgical Review Corporation in minimally invasive gynecologic surgery and multidisciplinary endometriosis care, and serves as Director of the Medcare Endometriosis Centre at Medcare Women & Children Hospital, the first multidisciplinary center of its kind in the UAE private sector.
As an experienced laparoscopic surgeon in Dubai, he pairs precise surgical technique with a coordinated team approach to address pain, fertility, and quality of life together.
Stop planning your life around your period. Book a consultation today.
FAQs
You generally cannot, and that is normal. It produces no distinct symptoms and is not visible on standard imaging. What can be assessed is whether your symptoms suggest endometriosis, through specialist examination, ultrasound or MRI, and where indicated, laparoscopy.
It occurs only while you are bleeding, so it spans the length of your period, usually two to seven days, and is most pronounced on the heaviest days of flow.
Symptoms often begin in adolescence, but diagnosis most commonly occurs between ages 25 and 35. An earlier assessment is preferable, as delay allows the disease to progress.
It is Sampson’s 1927 implantation theory: endometrial cells travel backward through the fallopian tubes into the pelvic cavity, implant on pelvic surfaces, and grow under hormonal influence to cause endometriosis.
Clinically, the menstrual cycle has four phases: the menstrual phase, the follicular phase, ovulation, and the luteal phase. Bleeding patterns are described separately, using terms such as normal, heavy, irregular, and absent menstruation.
About the Author
Dr. Charles Nagy, MD, FRCOG
Dr. Charles Nagy, is Director of the Medcare Endometriosis Centre and Associate Professor at the University of Sharjah. The first Middle East surgeon to achieve “Surgeon of Excellence” status (SRC, USA), he has 25+ years of expertise in minimally invasive gynecological surgery and fertility preservation.
As a Fellow of the Royal College of Obstetricians and Gynaecologists (FRCOG) and a member of AAGL, ESGE, BSGE, and BSCCP, he actively contribute to research, training, and the global exchange of knowledge in gynecologic surgery. He regularly present at international conferences and have authored and co-authored publications on minimally invasive surgery, endometriosis management, and reproductive outcomes.
His vision is to advance women’s health through precision surgery, compassionate care, and continuous education, and help train the next generation of gynecologic surgeons to carry that same commitment forward.
Medical Disclaimer
This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition.
Medically reviewed by Dr. Charles Nagy.