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The rationale for the IS-AIP becoming the IS-PAS

When the European Working Group on Abnormal Invasive Placenta (EW-AIP) started the world was in turmoil regarding what constituted the complex condition of abnormally adherent and invasive placenta (AAIP). Names rolled around the literature from ‘Morbidly Adherent Placenta’ (coined by a Scottish physician in 1885 for retention of cotyledons treated with opiate, ergot and brandy1) and ‘Placental Adhesive Disorders’ to the particularly inventive ‘Pernicious Placenta’. There is no doubt that this added to the confusion surrounding the condition resulting in poor diagnostic criteria, highly variable prevalence figures and deeply misleading published research.

Addressing this scientific chaos was one of the main reasons the EW-AIP was formed. Our central ethos being to improve worldwide understanding of AAIP and lead to improved outcomes for women globally. After much discussion the definition Abnormally Invasive Placenta (AIP) was reached and the International Society for Abnormally Invasive Placenta (IS-AIP) was born. We were aware that this only encompassed increta and percreta but given that we wanted to raise awareness regarding the end of the spectrum that was actually killing women, we were content to compromise with that.

Since then we have worked tirelessly to standardise definitions for this disorder including the Ultrasound2 and MRI3 signs then our recent mammoth undertaking to produce evidence-based guidelines4. To improve our worldwide standing and generate transparency, the working group became a society and our teaching and research work continued to blossom. Whilst we are becoming an internationally recognised voice for AAIP, we are not alone in our work. FIGO5 and other national societies such as the RCOG6 and SOCG7 have also acted to try to improve understanding of both researchers and coal-face clinicians. Swayed by the FIGO guidelines (which many of our members were involved in) the term Placenta Accreta Spectrum (PAS) has been rapidly adopted worldwide as it is the only term which covers the whole range of abnormally adherent and invasive placenta. FIGO has since gone on to classify PAS into grades8 (1= Accreta; 2= Increta; 3= Percreta). All of this is a positive step forward in the global understanding of the condition leading to better research, better education and better management of the women affected.

In light of this new nomenclature, our society once again reflected on our ethos of international collaboration and considered changing the name of the society. Having discussed it we voted and the new International Society for Placenta Accreta Spectrum (IS-PAS) was born. We remain committed to working on the invasive end of the spectrum but hope that this move goes towards unifying clinicians and academics worldwide.


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8th IS-PAS hybrid meeting in Athens, Greece May 2024 





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  1. Macdonald K. How to Prevent Septicaemia in Cases of Morbidly Adherent Placenta. Br Med J 1885;1268:779-80.
  2. Collins SL, Ashcroft A, Braun T, et al. Proposal for standardized ultrasound descriptors of abnormally invasive placenta (AIP). Ultrasound Obstet Gynecol 2016;47:271-5.
  3. Morel O, Collins SL, Uzan-Augui J, et al. A proposal for standardized magnetic resonance imaging (MRI) descriptors of abnormally invasive placenta (AIP) - From the International Society for AIP. Diagn Interv Imaging 2019;100:319-25.
  4. Collins SL, Alemdar B, van Beekhuizen HJ, et al. Evidence-based guidelines for the management of abnormally invasive placenta: recommendations from the International Society for Abnormally Invasive Placenta. Am J Obstet Gynecol 2019;220:511-26.
  5. Jauniaux E, Chantraine F, Silver RM, Langhoff-Roos J, Diagnosis FPA, Management Expert Consensus P. FIGO consensus guidelines on placenta accreta spectrum disorders: Epidemiology. Int J Gynaecol Obstet 2018;140:265-73.
  6. Jauniaux E, Alfirevic Z, Bhide AG, et al. Placenta Praevia and Placenta Accreta: Diagnosis and Management: Green-top Guideline No. 27a. BJOG 2019;126:e1-e48.
  7. Hobson SR, Kingdom JC, Murji A, et al. No. 383-Screening, Diagnosis, and Management of Placenta Accreta Spectrum Disorders. Journal of Obstetrics and Gynaecology Canada 2019;41:1035-49.
  8. Jauniaux E, Ayres-de-Campos D, Langhoff-Roos J, Fox KA, Collins S. FIGO classification for the clinical diagnosis of placenta accreta spectrum disorders. Int J Gynaecol Obstet 2019;146:20-24.