Placenta Accreta Spectrum (PAS): Diagnosis and Management

1.1    What are the risk factors for women with placenta accreta spectrum?

The major risk factors for placenta accreta spectrum are history of accreta in a previous pregnancy, previous caesarean delivery and other uterine surgery, including repeated endometrial curettage. This risk rises as the number of prior caesarean sections increases. (10-23)

[Strong recommendation, Moderate quality evidence]

Women requesting elective caesarean delivery for non-medical indications should be informed of the risk of placenta accreta spectrum and its consequences for subsequent pregnancies.  (24-26)

[GPS]

1.2 How can placenta accreta spectrum be suspected and diagnosed antenatally?

 Antenatal diagnosis of placenta accreta spectrum is crucial in planning its management and has been shown to reduce maternal morbidity and mortality. (27-30)

[Strong recommendation, Very Low-quality evidence]

Ultrasound assessment of placental location should be part of routine obstetric care, particularly in women undergoing cesarean section delivery.

[GPS]

Previous caesarean delivery and the presence of an anterior low-lying placenta or placenta praevia should alert the antenatal care team of the higher risk of placenta accreta spectrum. (29 & 31-34)

[Strong recommendation, Very Low-quality evidence]

1.2.1 Ultrasound screening and diagnosis of placenta accreta spectrum

Ultrasound imaging is highly accurate when performed by a skilled operator with experience in diagnosing placenta accreta spectrum.

Rational: In 2016, the European Working Group on Abnormally Invasive Placenta proposed a standardised description of ultrasound signs (see Appendix I) used for the prenatal diagnosis of placenta accreta and the International Abnormally Invasive Placenta Expert Group produced a proforma protocol for the ultrasound assessment.  (35&36)

[Strong recommendation, Low quality evidence]

Refer women with any ultrasound features suggestive of placenta accreta spectrum to a specialist unit with imaging expertise.

[Strong recommendation, Moderate quality evidence] 

Rational: The overall performance of ultrasound when performed by skilled operators is very good with a sensitivity of 90.72% (95% CI 87.2–93.6), specificity of 96.94% (95% CI 96.3–97.5) and diagnostic OR of 98.59 (95%CI 48.8–199.0). (37)

Women with a history of previous caesarean section seen to have an anterior low-lying placenta or placenta praevia at the routine fetal anomaly scan should be specifically screened for placenta accreta spectrum. (35-41)

[Strong recommendation, Very Low-quality evidence]

1.2.2 Is there a role for magnetic resonance imaging (MRI) in the diagnosis of placenta accreta spectrum?

Clinicians should be aware that the diagnostic value of MRI and ultrasound imaging in detecting placenta accreta spectrum is similar when performed by experts.  (42-45)

[Strong recommendation, Low quality evidence]

MRI may be used to complement ultrasound imaging to assess the depth of invasion and lateral extension of myometrial invasion, especially with posterior placentation and/or in women with ultrasound signs suggesting parametrial invasion. (45)

[GPS]

Women with a history of previous cesarean delivery or uterine surgery who are found to have an anterior low-lying placenta or placenta previa should be considered at increased risk for placenta accreta spectrum, even if imaging does not confirm the diagnosis.

[GPS]  

1.3 Where should women with placenta accreta spectrum be cared for?

Women diagnosed with placenta accreta spectrum should be cared for by a multidisciplinary team in a specialist centre with expertise in diagnosing and managing invasive placentation.

[GPS]

Rational

Women with accreta placentation should be cared for according to the risks of severe maternal bleeding and premature delivery. Placenta percreta can be associated with major prenatal complications from early in pregnancy, such as uterine rupture150–152 and bladder involvement with associated life-threatening haemorrhage. (27 & 46-49)

Prevention and treatment of anemia during the antenatal period is recommended for women with placenta praevia, a low-lying placenta or accreta as for any pregnant woman.  

[GPS]

 Delivery for women diagnosed with placenta accreta spectrum should take place in a specialist centre with logistic support for immediate access to blood products, adult intensive care unit and

NICU by a multidisciplinary team with expertise in complex pelvic surgery.

[Strong recommendation, Very Low-quality evidence] 

Rational: There is increasing evidence from retrospective cohort studies from the USA that women with placenta accreta spectrum diagnosed prenatally, cared for by a specialist multidisciplinary team, are less likely to require large volume blood transfusion and reoperation within 7 days of delivery for bleeding complications compared with women cared for by non-multidisciplinary standard obstetric care without a specific protocol.

In addition, maternal outcomes are improved over time with increasing experience within a well-established multidisciplinary team performing two to three cases per month.22 (27,28,50-54)

1.4 When should delivery be planned for women with placenta accreta spectrum?

In the absence of risk factors for preterm delivery in women with placenta accreta spectrum, planned delivery at 35⁺⁰ to 36⁺⁶ weeks of gestation provides the best balance between fetal maturity and the risk of unscheduled delivery.

[GPS]

Rational: Clinical factors should be considered when determining the timing of administration of antenatal corticosteroids and the optimal gestational age for delivery in women with placental accreta.

In cases of suspected placenta accreta spectrum, where significant blood loss and caesarean hysterectomy is anticipated, delivery at between 34 and 35 weeks of gestation has been proposed in order to avoid emergency delivery.

In the absence of risk factors for preterm delivery, it is safe to plan the delivery at 36 weeks of gestation. Urgent delivery for bleeding decreases significantly with advancing gestation. Those with no risk factors for preterm birth are at low risk for an unscheduled delivery prior to 36 weeks of gestation. (55-60)

2. Planning delivery of women with suspected placenta accreta spectrum:

Once the diagnosis of placenta accreta spectrum is made, a contingency plan for emergency delivery should be developed in partnership with the woman, including the use of an institutional protocol for the management of maternal haemorrhage.

[GPS]

Rational: Due to a lack of RCTs or well-controlled observational studies, the optimal management of placenta accreta spectrum remains undefined and is determined by the expertise available, the depth and lateral extension of the accreta portion of the placenta, the presence of an associated placenta praevia, radiological findings, the medical and surgical comorbidities, and finally, the accessibility of a regional team focused on these patients. (61-65)

2.1 What should be included in the consent form for caesarean section in women with suspected placenta accreta spectrum?

Any woman giving consent for caesarean section should understand the risks associated with caesarean section in general, and the specific risks of placenta accreta spectrum in terms of massive obstetric haemorrhage, increased risk of lower urinary tract damage, the need for blood transfusion and the risk of hysterectomy. (62)

[Strong recommendation, Very low quality evidence]

Additional possible interventions in the case of massive haemorrhage should also be discussed, including cell salvage and interventional radiology where available. (66)

[Conditional recommendation, low quality evidence]

2.2 What healthcare professionals should be involved?

The elective delivery of women with placenta accreta spectrum should be managed by a multidisciplinary team, which should include senior anaesthetists, obstetricians and gynaecologists with appropriate experience in managing the condition and other surgical specialties if indicated. In an emergency, the most senior clinicians available should be involved.

[Strong recommendation, Very low quality evidence]

Rational: The UK National Patient Safety Agency in collaboration with the RCOG and the Royal College of Midwives set up an expert working group to develop a care bundle for placenta accreta.173 Six elements of good care were agreed upon. The care bundle was then tested in six units over a 5-month pilot study period, and it was found to be both achievable and practical.

The six elements considered to be reflective of good care are(67):

·  Consultant obstetrician planning and directly supervising delivery.

·   Consultant anaesthetist planning and directly supervising anaesthesia at delivery.

·  Blood and blood products available.

·  Multidisciplinary involvement in preoperative planning.

· Discussion and consent, including possible interventions (such as hysterectomy, leaving the placenta in situ, cell salvage and interventional radiology).

·  Local availability of a level 2 critical care bed.

2.3 What anaesthetic is most appropriate for delivery?

The choice of anaesthetic technique for caesarean section for women with placenta accreta spectrum should be made by the anaesthetist conducting the procedure in consultation with the woman prior to surgery. (68)

[GPS]

The woman should be informed that the surgical procedure can be performed safely with regional anaesthesia but should be advised that it may be necessary to convert to general anaesthesia if required and asked to consent to this.

[GPS]

Rational: Both general and regional anaesthetic techniques have been shown to be safe for surgical procedures required for the delivery of placenta accreta spectrum; the judgment of which type of technique to be used should be made on an individual basis. (68)

2.4 Optimizing the delivery of women with placenta accreta spectrum:

2.4.1 What surgical approach should be used for women with placenta accreta spectrum? 

Intravenous tranexamic acid should be administered at the commencement of surgery because it reduces intraoperative blood loss

[strong, high-quality evidence]

Rational: Tranexamic acid is a widely available hemostatic antifibrinolytic agent that inhibits the enzymatic breakdown of fibrinogen and fibrin by plasmin. Significant international efforts have culminated in several studies investigating tranexamic acid in obstetric trauma and postpartum hemorrhage. Most recently, a large double- blind placebo- controlled trial recruited over 20 000 patients with postpartum hemorrhage to the WOMAN trial. The study demonstrated that, compared with placebo, tranexamic administration significantly reduced death due to massive obstetric hemorrhage without increasing rates of adverse events, including thromboembolism. A recent meta- analysis of nine trials involving 2365 patients confirmed these findings, demonstrating that the administration of tranexamic acid before cesarean delivery significantly reduces intra- and postoperative blood loss and blood transfusion with no increase in thromboembolic events. After this analysis, three more placebo-controlled trials have shown that tranexamic acid administration immediately before cesarean delivery significantly reduces reported intraoperative blood loss and postoperative declines in hemoglobin without any increase in adverse maternal or neonatal effects, No trials have specifically examined the role of tranexamic acid in the surgical management of PAS disorders. However, the quality of the evidence on postpartum hemorrhage justifies its use in the management of women diagnosed prenatally or presenting with PAS disorders at the time of delivery. (69-72)

Caesarean section hysterectomy with the placenta left in situ is preferable to attempting to separate it from the uterine wall.

[ strong, Very low-quality evidence]

Rational: The ACOG recommends planned, preterm caesarean section hysterectomy with the placenta left in situ as removal of a placenta accreta spectrum is associated with significant haemorrhagic morbidity. In cases of high suspicion for accreta during caesarean delivery, the majority of members of the US Society of Maternal-Fetal Medicine (SMFM) and FIGO expert panel proceed with hysterectomy.

A retrospective study of 57 cases of suspected accreta demonstrated significantly reduced short-term morbidity if the placenta is left in place and hysterectomy is performed electively compared with attempting to remove the placenta first. Attempting placental separation risks hysterectomy in up to 100% of cases as also confirmed by other authors. (74-78)

When the extent of the placenta accreta is limited in depth and surface area, and the entire placental implantation area is accessible and visualised (i.e. completely anterior, fundal or posterior without deep pelvic invasion), uterus preserving surgery may be appropriate, including partial myometrial resection.

[conditional, Very low- quality evidence]

 Rational: A small cohort study has shown that the introduction of the Triple-P procedure [perioperative placental localisation, pelvic devascularisation and placental non-separation] involving delivery of the fetus via transverse uterine incision above the upper border of the placenta, myometrial excision and reconstruction of the uterine wall reduces the rate of hysterectomy, PPH and duration of hospital stay in women with placenta accreta. The incidence of postoperative complications of the Triple-P procedure depends on comorbidities and in particular, the placental position and the depth of villous invasion. Small case series have also reported on the successful use of compression sutures and on using the cervix as a natural tamponade by inverting it into the uterine cavity and suturing the anterior and/or the posterior cervical lips into the anterior and/or posterior walls of the lower uterine segment.

 A systematic review found that uterus preserving surgery resulted in a secondary hysterectomy in 24/77 women (31%), maternal mortality in 2/55 women (4%), subsequent menstruation in 28/34 women (82%) and subsequent pregnancy in 19/26 women (73%). A more recent systematic review showed that uterus preserving surgery is associated with a success rate of 48/76 women (63.2%), a secondary hysterectomy in 23/76 women (30.0%), maternal mortality in 2/54 women (3.7%), subsequent menstruation in 20/37 women (81.1%) and subsequent pregnancy in 21/27 women (77.8%). (79-82)

Uterus preserving surgical techniques should only be attempted by surgeons working in teams with appropriate expertise to manage such cases and after appropriate counselling regarding risks and with informed consent.  (79-84)

[conditional, Very low-quality evidence]

There are currently insufficient data to recommend the routine use of ureteric stents in placenta accreta spectrum. The use of stents may have a role when the urinary bladder is invaded by placental tissue.

[GPS]

Rational: There are no RCTs on the use of ureteric stents in placenta accreta spectrum. Ureteric stents or catheters are more commonly used preoperatively in the USA where around 26% of the members of both the SMFM and ACOG fellows are using them in the management of suspected abnormally invasive placenta. (85&86)

2.4.2 What surgical approach should be used for women with placenta percreta? 

There is limited evidence to support uterus preserving surgery in placenta percreta and women should be informed of the high risk of peripartum and secondary complications, including the need for secondary hysterectomy.

[GPS]

 Rational: There are no well-controlled observational studies, and therefore, no firm recommendations can be made.

The following four approaches have been described.

1.  Primary hysterectomy following delivery of the fetus, without attempting placental separation.

2. Delivery of the fetus avoiding the placenta, with repair of the incision leaving the placenta in situ

3. Delivery of the fetus without disturbing the placenta, followed by partial excision of the uterine wall (placental implantation site) and repair of the uterus.

4.  Delivery of the fetus without disturbing the placenta, and leaving it in situ, followed by elective secondary hysterectomy 3–7 days following the primary procedure.

There are no well-controlled observational studies, and therefore, no firm recommendations can be made. (85-90)

2.5 When is interventional radiology indicated?

Larger studies are necessary to determine the safety and efficacy of interventional radiology before this technique can be advised in the routine management of placenta accreta spectrum.

[strong, Very low-quality evidence]

Rational: Studies evaluating the safety and efficacy of interventional radiology in assisting surgical and conservative management of placenta accreta with variable success are very heterogeneous with no data on the diagnosis of the different grades of villous invasion and variable confounding factors, such as placental position and number of previous caesarean deliveries. (91-107)

Women diagnosed with placenta accreta spectrum who decline donor blood transfusion should be cared for in a unit with an interventional radiology service.

[Conditional, Very low quality evidence]

2.6 How are women with undiagnosed or unsuspected placenta accreta spectrum best managed at delivery?

If at the time of an elective repeat caesarean section, where both mother and baby are stable, it is immediately apparent that placenta percreta is present on opening the abdomen, the caesarean section should be delayed until the appropriate staff and resources have been assembled and adequate blood products are available. This may involve closure of the maternal abdomen and urgent transfer to a specialist unit for delivery.

[GPS]

 In case of unsuspected placenta accreta spectrum diagnosed after the birth of the baby, the placenta should be left in situ and an emergency hysterectomy performed.

[GPS]