Abnormally Invasive Placenta – AIP. Awareness and pro‐active management is necessary

This theme issue focuses a serious and important topic in obstetrics and feto-maternal medicine: abnormally invasive placenta (AIP). Abnormally invasive placenta (AIP) is a broad term that covers conditions where the placenta is a true accreta, increta or percreta. To draw a line between these entities in the clinical situation, where the invasiveness of the placenta is not always known in advance, is not easy. Even after delivery the diagnosis is a challenge, except when the uterus is removed and examined by the pathologist, which is considered as the gold standard examination to classify AIP cases. The reason why we introduce the broad term abnormally invasive placenta (AIP) is that “placenta accreta” has been used with different definitions in the literature. The term placenta accreta originates from histopathology and defines the direct attachment of placental villi to the myometrium without intervening decidua. Depending on the depth of trophoblast invasion into the myometrium, three subtypes are differentiated by the pathologist: placenta accreta vera, increta and percreta. In placenta accreta vera, chorionic villi attach directly to the myometrium in the absence of decidua. In placenta increta, placental villi invade deeper into the myometrium, but do not extend to the outermost layers of the uterus. In placenta percreta, chorionic villi penetrate through the myometrium up to the serosa. The neo-vascularization caused by the growing placenta percreta may soften the tissues of the adjacent organs (bladder, intestines, parametrium and other neigboring tissues) and simulate invasion. But the placental tissue usually respects the serosa, unless it, – in rare cases, tenderizes or softens up the serosa, which may lead to eventual symptomatic uterine rupture. The problem is that the term “accreta” is used to describe different specific grades of abnormal placental infiltration from accreta to percreta, and at the same time it is used as a general term. Therefore, we believe that another general term for these conditions will be helpful. We propose a clinical definition of “abnormally invasive placenta” (AIP): a placenta that cannot be removed spontaneously or manually, without causing severe bleeding. Most articles on AIP report a mixture of cases of placenta accreta, increta and percreta, which makes it difficult to assess the results with regard to management of each single entity. Placenta percreta is the most serious of the abnormally invasive placentas and associated with a significant risk of severe maternal morbidity and mortality. The main problem of severe AIP is the elevated maternal morbidity and even mortality due to live-threatening bleeding at (forced) placental delivery if the condition is not suspected beforehand. The strong association between a previous cesarean delivery and AIP means that with the rise in cesarean section rates, seen in a an almost world-wide context 1, we will experience more cases of AIP in the future 2, 3. Only few studies have documented this, mostly because of a lack of longitudinal studies and the variation in use of the diagnosis of AIP. Still the frequency of severe AIP seems to have risen maybe 10 times over the last 50 years and approximately 1/500 to 1/2500 deliveries is complicated by AIP 4, 5. AIP is caused by a disturbed dialog between the decidua and trophoblast at the moment of implantation and placental development. Some authors argue that the infiltrating trophoblast is too “aggressive”, but most experts presume that the etiology is an incompetent or absent decidua caused by endometrial damage or trauma, caused by surgery like cesarean section or curettage, hysteroscopic operations, infections or irradiation of the uterus. Fibrosis in scar tissue may also be involved. Fundamental research in this field is still needed to achieve a full understanding of the etiology of AIP and possibly prevention of the development of AIP. A key factor in AIP management is the prenatal diagnosis. Only by this could delivery be planned in ideal conditions at a referral centre with the necessary additional and back-up services, so that the maternal risks could be significantly reduced. Prenatal diagnosis of AIP is challenging but feasible, if the ultrasonographer is searching actively for the well-described ultrasonic signs. In women presenting a low-lying placenta and a history of uterine surgery, the ultrasonographer has to be even more cautious. In cases of doubt, especially when the placenta is posterior, magnetic resonance imaging (MRI) will be helpful. Usually, women with signs of severe AIP are hospitalized after a bleeding episode, and some are hospitalized for several weeks from the time of diagnosis until planned cesarean delivery. There is a slight risk of catastrophic intra-abdominal bleeding from the AIP perforating the serosa, which may motivate this hospitalization. In several studies it has been observed that the planned (elective) cesarean delivery is associated with less maternal morbidity and mortality than emergency cesarean delivery. A decision analysis considering maternal and fetal complications indicated that the optimal time for planned cesarean section is about 34–36 weeks 6, 7. At the planned cesarean delivery, a multi-professional approach is extremely important. We need help from our friends, experts in hemostasis, anesthesiology, radiological intervention and even immediate access to urologists, gastrointestinal surgeons and neonatologists. We also value a pro-active attitude from our colleagues. The blood packages should be in the operation theater at the start of the operation and two surgical assistants should be prepared to support. The obstetrician should have a primary, secondary and even a tertiary plan and still be prepared for a change of plans during surgery. Also, the obstetrician should be the designated team leader respected by everyone on site throughout the collaborative effort. In general, there are three main approaches after delivery of the infant through an incision that does the least damage to the placenta. The traditional mode is the peripartum hysterectomy. Many have engaged in the conservative mode: leaving the placenta in situ. Some experienced obstetricians recommend local resection of the percreta area. The modes may be combined and used sequentially. Leaving the placenta in situ sometimes leads to sepsis and secondary hemorrhage, resulting in ultimate hysterectomy. Also, the diagnosis of severe AIP or placenta percreta is often first made when entering the abdominal cavity, when the signs of percreta on the surface of the isthmic segment are seen. In those cases it may be a wise decision to deliver the infant, leave the placenta, close the uterus and book the woman for second surgery (local resection or hysterectomy) at a later time and/or at another more resource-advanced hospital. All the hemostatic interventions have potentially adverse effects. Radiological balloons may initiate thrombosis and radiological embolization may result in inappropriate ischemia and neurological complications. Even the popular B-Lynch sutures are associated with complications, and a combination of transverse and vertical sutures may cause uterine ischemia. Therefore local manual compression with tamponade for some time, or even aortic compression, may be advantageous. Modes of management or specific interventions can never be expected to become strictly evidence-based. There are several reasons for that: AIP cases are rare; it is a heterogeneous group of patients with different grades of AIP; the individual patients differ in attitudes to future fertility and menstruations, which will influence the intended mode of delivery; the available resources differ; and the personal experience among experts, although limited, sometimes results in “schools of thought” where preferences based on beliefs and experiences exist. The limited experience obtainable in most centers means that we have to share our experience in structured presentations. Ideally, in controlled trials, which are difficult to perform properly. Also, if we structure our clinical treatment too much, as necessary in a prospective controlled trial, we limit ourselves with regard to rational changes in choice and sequence of interventions and most importantly with a view to continuous improvement. We therefore have to acknowledge that publications of consecutive case series with historical and geographical controls, admittedly with a high level of potential bias, is sometimes the best evidence we can expect to get in the field of AIP management. Considering that severe AIP is an uncommon condition we need to institute and support international prospective consecutive data collection (International Obstetric Surveillance System (INOSS) and European Working group on Abnormal Invasive Placenta (EW-AIP)), using a standardized protocol including information on intended as well as actual management, documented with pictures and possibly even videos, as well as information on long-term follow-up. Since each case of AIP is different the clinical management should probably be taylor-made to optimize results considering the woman's wish for a future pregnancy, the obstetrician's experience as well as radiological and surgical resources. In line with this concept the New England Medical Journal has recently chosen to publish a single case report as a narrative with experts' views on considerations and arguments in a specific case 8. To share knowledge and experience, difficult cases should be discussed as they come up between experts in an international network. Even if the incidence of severe AIP increases due to the rising rates of cesarean section, it is still a “rare” event. Therefore, it is important to train obstetricians and sonographers in the prenatal diagnosis of AIP in order to organize timely referral to an institution familiar with the management of severe post-partum hemorrhage. Indeed, a multidisciplinary approach including obstetricians, anesthesiologists, pelvic surgeons, radiologists, a blood bank and an intensive care unit is mandatory to provide optimal healthcare. Those who locally are best at managing the situation should be designated. Also, referral centers should collaborate in exchanging knowledge or in sharing a common database. In doing so, it would be possible to register prospectively data from a large cohort to confirm or to improve current knowledge of the optimal clinical management of severe AIP. In Europe we have a great opportunity to build such a collaborative group and a collect material in a multicenter study. Distances between patients, referring healthcare providers and “specialized AIP centers” are short and could be easily overcome by car or by plane. In 2012, a working group of 20 experts from eight European countries met several times to launch the EW-AIP project (European Working group on AIP), due to be done in 2013. The aim is to improve prenatal diagnosis, peripartum management and the understanding of pathophysiology. Severe AIP-cases should be managed in a few reference centers to reduce the maternal morbidity and mortality. After a special session on AIP at the 9th Congress of the European Society of Gynecology in Copenhagen (September 2011), the AOGS Editors recognized the importance of AIP and decided to publish a theme issue. The call for contributions was such a success that only a selection of accepted papers could be published in the theme issue. The other articles will be published in the nearest future in the journal. The focus of this issue is to inform about the actual knowledge in prenatal diagnosis and peripartum management of severe AIP by some overviews written by experts and to provide a platform for research articles. Together they will inform you about the state of the art and propose research strategies for the future. Still, the cases of severe AIP are uncommon and in the striving to become a real expert in diagnosis and treatment of severe AIP it is not an option to wait for proper prospective and controlled trials. Be aware that vessels that supply the severe AIP are not those published in old anatomical or obstetrical textbooks. Pro-active collaboration is essential to plan a safe delivery, and participation in a European project with prospective registration and monitoring will add to our common knowledge.