Retrograde Menstruation Theory

The retrograde menstruation theory is a long-held explanation of how endometriosis begins. During a period, some blood and tissue flow backward through the fallopian tubes. The theory proposes that this tissue reaches the abdominal cavity, attaches, and grows. The idea first appeared in 1925.¹ Dr. John Sampson set out the full theory in a 1927 paper.² It has shaped medical thinking about endometriosis ever since.

The theory still explains part of the picture. Retrograde flow is common. Studies suggest that 76 to 90 percent of women have some retrograde flow. Yet most of these women never develop endometriosis.¹ This gap is the first sign that retrograde flow is only part of the explanation.

The second sign is location. Retrograde flow can explain disease on the ovaries and on the peritoneum, the thin lining of the abdomen. Fluid circulates within the abdomen. Tissue can therefore also reach the underside of the diaphragm. Retrograde flow cannot explain disease outside the abdomen. Endometriosis has appeared in the pleura, the lining of the chest, and even in nerves.¹ Those sites require another explanation.

The third sign comes from before birth. One study examined 52 female fetuses at autopsy. It found endometriosis in 4 of them.³ This finding fits a different idea, the embryonic rest theory. Under this theory, tissue may become misplaced while the body forms before birth. Retrograde flow cannot explain tissue that is present before a girl has had a first period.

The fourth sign is that men can rarely develop endometriosis. Most reported cases involved long-term estrogen treatment.⁴ Men do not menstruate. Retrograde flow therefore cannot be the cause in these cases.

No single theory explains every case. Researchers study several other ideas. Normal cells lining the abdomen or chest may change into cells that resemble the uterine lining (coelomic metaplasia). Cells left in the wrong place during early development may remain there. Stem cells from the uterus or bone marrow may travel and settle in new places. Tissue may also spread through lymph or blood vessels.¹ More than one of these can be true at once. Different causes may drive disease in different parts of the body.

This distinction matters for care. Endometriosis is living tissue with its own blood supply. It can grow and spread over time (disease progression). Stopping periods does not remove it. The excision surgery entry and the broader endometriosis overview cover treatment. A view of endometriosis as only a menstrual problem points care in the wrong direction.

The theory still helps explain how some disease on the ovaries and peritoneum may begin. Treating it as the full answer, however, has cost patients for decades. It pushed care toward suppressing the cycle instead of treating the disease. It left women with disease in unusual locations without a clear answer. Knowledge of its limits helps explain why endometriosis is so often missed and undertreated. For a related condition that shares some of the same causes, see adenomyosis.