Other than the 3 types of disease, we also have stages of endometriosis. As we now know, endometriosis is a heterogeneous disease and, therefore, staging of endometriosis is not always an easy task. This is why there are, up to this date, more than one staging systems of endometriosis. The 3 most commonly used are:

1. The revised ASRM Classification System (rASRM)¹: Developed in 1996, it remains the most commonly used classification system. It classifies the disease in stages depending on the key features of endometriosis lesions. There is no direct correlation between the stage of the disease and the severity of symptoms or the likelihood of conception.

• Enzian Classification System²: Introduced in Austria in 2005. It is superior in the detailed classification of deep endometriosis (type 3). It was revised and republished (#ENZIAN) in 2021³.

Although the purpose of this text is not to describe this classification system in great detail, the letter refers to the anatomical location of the lesion and the number to the size. It also conveys the benefit of correlating between the pre-operative ultrasound (or MRI) findings and the findings during surgery (laparoscopy)⁴. Neither this classification system, though, predicts the severity of symptoms or the chances of natural conception⁵.

• Endometriosis Fertility Index (EFI)⁶: The purpose of this index is to predict the likelihood of natural conception in women with endometriosis.

The pregnancy rates are 8.3% in women with EFI of 0 to 3, 41.2% for 4 to 7 and 60.9% for 8 to 10⁷. It can also be useful in predicting the likelihood of success of IVF⁸. It is also not associated with the severity of symptoms and is more complex to use.

In conclusion, there are different staging systems, without any of them being clearly superior to the others. Most gynaecologists use the rASRM⁹, whilst EFI is superior in predicting pregnancy rates. The biggest problem remains the lack of correlation between the stage of the disease and the severity of symptoms. There exists the need for a new classification system that will predict the type and severity of symptoms and will be user-friendly.

References:

1. Revised American Society for Reproductive Medicine classification of endometriosis: 1996. Fertil Steril. 1997;67:817–21.
2. Tuttlies F, Keckstein J, Ulrich U, Possover M, Schweppe KW, Wustlich M, et al. ENZIAN-score, a classification of deep infiltrating endometriosis. Zentralbl Gynakol. 2005; 127:275–81.
3. Keckstein J, Saridogan E, Ulrich UA, Sillem M, Oppelt P, Schweppe KW, Krentel H, Janschek E, Exacoustos C, Malzoni M, Mueller M, Roman H, Condous G, Forman A, Jansen FW, Bokor A, Simedrea V, Hudelist G. The #Enzian classification: A comprehensive non-invasive and surgical description system for endometriosis. Acta Obstet Gynecol Scand. 2021 Jul;100(7):1165-1175.
4. Di Paola V, Manfredi R, Castelli F, Negrelli R, Mehrabi S, Pozzi Mucelli R. Detection and localization of deep endometriosis by means of MRI and correlation with the ENZIAN score. Eur J Radiol. 2015;84:568–74.
5. Johnson NP, Hummelshoj L, Adamson GD, Keckstein J, Taylor HS, Abrao MS, et al. World Endometriosis Society consensus on the classification of endometriosis. Hum Reprod. 2017;32:315–24.
6. Adamson GD, Pasta DJ. Endometriosis fertility index: the new, validated endometriosis staging system. Fertil Steril. 2010 Oct;94(5):1609-15.
7. Zeng C, Xu JN, Zhou Y, Zhou YF, Zhu SN, Xue Q. Reproductive performance after surgery for endometriosis: predictive value of the revised American Fertility Society classification and the endometriosis fertility index. Gynecol Obstet Invest. 2014;77:180–5.
8. Wang W, Li R, Fang T, Huang L, Ouyang N, Wang L, et al. Endometriosis fertility index score maybe more accurate for predicting the outcomes of in vitro fertilisation than r-AFS classification in women with endometriosis. Reprod Biol Endocrinol. 2013;11:112.
9. International Working Group of AAGL, ESGE, ESHRE and WES, Zondervan KT, Missmer S, Abrao MS, Einarsson JI, Horne AW, Johnson NP, Lee TTM, Petrozza J, Tomassetti C, Vermeulen N, Grimbizis G, De Wilde RL. Endometriosis classification systems: an international survey to map current knowledge and uptake. Hum Reprod Open. 2022 Mar 1;2022(1):hoac002