Placenta accreta spectrum is one of the greatest challenges we see as modern obstetricians. Whilst it may be infrequent, its incidence is rapidly increasing, and we are becoming acutely more aware of the risk it poses to our patients and their families. This article will share our thoughts and processes from South Australia for our unique team-based structure for our local maternity consumers.

Placenta accreta refers to pathologically abnormal adherence and invasion of trophoblastic tissue into the uterine wall. There are several proposed aetiologies for development, however the currently preferred pathological theory is infiltration of trophoblastic tissue beyond the decidua basalis, usually at the site of a scar or other form of endometrial-myometrial defect. This results in a placenta that is “morbidly adherent” to the uterine wall, with failure of separation at the time of delivery.¹ There is a spectrum of disease from minor adherence to involvement of deeper structures and newer conversations encompassing caesarean scar ectopic pregnancies as the first trimester presentation of this condition.

There have been recent updates to the definition and classification of the placenta accreta system, with a new consensus and histopathological grading system released in 2019:

• Grade 1: Non-invasive – adherent placentation without invasion.
• Grade 2: Superficial invasion – myometrial involvement with preservation of >25% wall thickness.
• Grade 3A: Deep invasion – myometrial involvement with <25% of wall thickness remaining, serosa intact.
• Grade 3D: Deep invasion with disruption of the serosa.
• Grade 3E: Deep invasion with adherence to extrauterine structures and adjacent organs.^2,3

Incidence of placenta accreta spectrum has been gradually increasing over the 20^th and 21^st centuries. Studies from the United States during the 1970s placed the incidence at one in 4027 (0.02%).⁴ This figure rose to one in 588 (0.17%)⁵ in 2010 and was most recently published at one in 272 (0.37%)⁶ in 2016. This increase is dramatically important for us as Australian obstetricians, with a greater need for access to timely, experienced clinicians in our tertiary centres, and greater need for awareness and training for all obstetricians in all centres who may be faced with undiagnosed cases in acute emergencies. Changes in modern obstetrics are likely responsible for this steady increase, particularly the increase in the rate of caesarean births, with a rise in caesarean birth rates from 6.4% in Sydney in 1970⁷ to 41% of births in Australia last year.⁸ We have also seen an increase in the rates of IVF pregnancies, a greater awareness of Asherman’s syndrome, and pregnancies conceived after radiation therapy or endometrial ablation. The increasing prevalence and need for complex management for those affected by PAS was reflected in RANZCOG’s consensus guidelines(opens in new tab) published in March 2023, with recommendations for discussion at a multidisciplinary team (MDT) meeting following diagnosis.⁹

Management of placenta accreta is highly individualised and based on the degree of abnormal placentation, the patient’s needs and wishes, and preferred surgical approaches undertaken by each specific team. The general principles encompass antenatal identification, work up and surgical optimisation, prioritising elective delivery where possible, and uterine entry away from the site of the placenta. In reality, this may require a midline abdominal incision or extended transverse abdominal incision, with a focus on attaining appropriate access prior to birth of the baby. Cases where there is a concern for bladder involvement or need for hysterectomy may require urology input and insertion of ureteric catheters. Interventional radiology may be used for intraoperative or postoperative haemorrhage control at the discretion of the team.

In South Australia, we have created a specific Placenta Accreta Spectrum Team and MDT. Our state has around 19,500 births annually, with close to 12,000 of these being in metropolitan teaching hospitals.¹⁰ Tertiary services are spread over three major metropolitan hospitals (the Lyell McEwin Hospital, Women’s and Children’s Hospital, and Flinders Medical Centre), however we are uniquely challenged in that only one site has a level 6 nursery and co-located full adult ICU. For this reason, we aim for all high-risk scheduled PAS births to occur at Flinders Medical Centre. Our service involves a rotating small group of O&G consultants with a specific interest in this area, as well as a senior registrar position each year.

Our MDT comprises each of the O&G consultants involved in regular PAS births from each of the tertiary centres. The team also includes anaesthetics, radiology, and interventional radiology, with neonatology, urology, gynaecological oncology, ICU, vascular surgery, and other specialties as requested on a case-by-case basis.

Referrals to our service come through each of the tertiary centres, as well as from the Northern Territory and private obstetricians. Our MDT runs every four weeks, and all new cases are presented in detail with imaging reviewed by the whole team. The team then creates a plan for antenatal care and birth. Upcoming appointments are created to ensure patients have seen relevant team members and anaesthetics throughout the journey, to allow for appropriate patient support, counselling, and optimisation. Further required imaging is ordered, and goals for birth are planned. Birth planning is detailed, including aims for mode of birth, gestation, location, team members required, surgical approaches, and need for ureteric catheters, interventional radiology, and ICU support. The plan is then documented and uploaded to Sunrise, the SA Health Electronic Medical Record, so that it may be accessed by any SA Health site in the event of an emergency. Not all patients referred to the MDT will be delivered at Flinders Medical Centre, with opinions also being sought for reassurance or to plan moderate risk births at other tertiary sites or within private hospitals with appropriate team members present.

The day of birth may involve a large team for high-risk cases, and we will usually arrange for two of our consultant O&Gs to work together for planned caesarean hysterectomies, as well as making sure we have one of our core high-risk obstetric anaesthetic staff, urology, and interventional radiology teams as required. It is a huge day for our patients, and we will often make sure we are there with them early to help them navigate this day and to try to provide some continuity throughout the journey.

The MDT will review outcomes following birth for each of our patients, including the timing, mode, and outcome of birth, as well as estimated blood loss and any complications for mother or baby. We will also review placental histology and reflect on whether we were happy with our antenatal assessment and plan. We will review whether there were any opportunities to improve the outcome for the patient and their family. Finally, we have added a section reviewing caesarean scar ectopic pregnancies, management, and progress. All cases discussed at the meeting are done so with consent from the individuals involved, and meeting feedback is fed back through our team or their referring doctor.

Whilst the incidence of PAS may be increasing, the approach to diagnosis and management appears to be subtly changing. There is increasing international interest around uterine conservation surgery, as well as alternative interventional radiology techniques. There are large centres in Indonesia and Colombia leading many discussions around uterine conservation, as well as centres within the USA, Europe, and the UK trialling alternative approaches to improve patient safety. Although Australia has a small population and therefore lower case volumes, we have yet to establish a formal Australian network for centres involved in PAS to collaborate in data, approaches, and outcomes. We are aware that the team-based management of PAS in the eastern states of Australia is quite different to what we have described here, and also of differences in Perth, and wonder if it may be time to create collegiate links across the country for those of us regularly involved in providing these services.

If you are a regular PAS provider and are interested in opening this conversation with our team, please get in contact via [email protected].