Stages of Endometriosis

Reviewed by: HU Medical Review Board | Last reviewed: June 2018

If you are diagnosed with endometriosis, you may also receive more information on the characteristics of your condition. Each case of endometriosis can vary in severity, classification, symptoms, and defining features. Some of the most recognized forms of endometriosis are superficial peritoneal endometriosis, ovarian ovarian endometriomas, and deep infiltrating endometriosis, however, this is not an exhaustive list of all of the ways endometriosis can present. Also, within each of these classifications exists a sliding scale of severity as well. It's also possible to have multiple types of endometriosis at once.1-3

One thing that is important to note, however, is that the type or severity of endometriosis present does not always correlate to the symptoms an individual experiences. For example, someone with mild superficial peritoneal endometriosis may experience more pain or physical symptoms than someone else with more severe, deep infiltrating endometriosis. Despite these differences, you most likely will receive a staging classification for your endometriosis. This is to allow your provider to track how your endometriosis is changing over time on a commonly used scale. The stages of endometriosis refer to the condition itself, while another metric, the Endometriosis Fertility Index, is a tool used to predict the likelihood that a woman with endometriosis will become pregnant.

The Four Stages of Endometriosis

The current staging method of endometriosis is based on guidelines outlined by the American Society for Reproductive Medicine (ASRM).4 The stages range from I (one) to IV (four), with I being the most mild and IV being the most severe. Again, these stages do not necessarily correlate with the symptoms experienced, as a woman with stage IV may be asymptomatic (experience no symptoms), while a woman with stage I may experience debilitating symptoms. Endometriosis is staged based on the location, depth, and extent of endometriosis lesions, the size and presence of any endometriomas (endometriosis-related ovarian cysts), the severity of any adhesions present (bundles of scar tissue that can adhere pelvic structures to one another), and any endometriosis-related blockages within the fallopian tubes. Each factor is scored, with higher scores indicating more advanced progression. The score breakdown is roughly as follows:

  • Stage I: Minimal endometriosis with a score of 1-5 on the ARSM scale. Endometriosis of this type generally has superficial lesions, with very few, if any, small, deep lesions. Typically, endometriomas are not present, and any adhesions found are mild and filmy in nature.
  • Stage II: Mild endometriosis scoring 6-15 points on the scale. Stage II endometriosis has many of the same characteristics as stage I, however, these are slightly more progressed. Stage II endometriosis may also be more widespread than stage I, affecting more areas of the pelvis, including the space between the anus and the vagina.
  • Stage III: Moderate endometriosis with a score of 16-40 points. Stage III has all of the same features of stage I and II, however, these are markedly more severe. Endometriomas are often present, and adhesions are extensive and dense. More endometriosis lesions are deeply infiltrating rather than primarily superficial.
  • Stage IV: Severe endometriosis scoring 40 points or more. Stage IV endometriosis has all of the characteristics of stages I-III, however, adhesions are so severe and dense that they can connect structures to one another such as the ovaries to the fallopian tubes, along with other structures that should not be united. This prevents proper functioning and restricts internal movement. The fallopian tubes may even become completely enclosed by adhesions, greatly impacting fertility.3-5

Endometriosis Fertility Index (EFI)

The ASRM staging guidelines were originally created to predict the fertility of a woman with endometriosis, however, a new system, the Endometriosis Fertility Index (EFI) has arisen for this purpose, and the ASRM system is used to classify condition progression as a whole. It has been theorized that the Endometriosis Fertility Index is a more reliable predictor of the possibility of becoming pregnant after surgical treatment of endometriosis when compared to the ASRM system. Because of this, many providers will use the EFI when determining a woman's chances of becoming pregnant post-endometriosis surgical treatment.6

The EFI takes into account the functional status of the fallopian tubes, ovaries, and fimbriae (fingerlike projections that help facilitate egg movement from the ovaries to the fallopian tubes before potential fertilization). Additionally, the EFI takes into account a woman's age, amount of time she has been experiencing infertility, if she has been pregnant before, and her ASRM score. All of these together create one number on a scale of zero to ten. The closer to ten a woman scores, the higher the chances that she will become pregnant.6 If you have endometriosis and are thinking about pregnancy, or trying to become pregnant currently, ask your provider for more information on your EFI score and fertility chances.

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