Definition Placenta accreta spectrum (PAS) disorders (formerly called abnormal invasion of the placenta or morbidly adherent placenta) refers to the abnormal invasion of trophoblastic tissue beyond the decidua basalis into the uterine myometrium, the uterine serosa or even beyond, involving adjacent pelvic organs. This is believed to be caused by damage to the decidua basalis that allows the invasion of the placental tissue deeper into the myometrium and beyond. Depending on the degree of trophoblastic invasion, it is classified into
Accreta, the placenta invades <50% of the myometrium (78% of the cases)
Increta, invades >50% of the myometrium (17% of the cases)
Percreta, placenta perforates the uterine serosa and spreads to other pelvic organs (5% of the cases)
Incidence There has been an increasing incidence from 1 in 2500 deliveries to 1 in 533 deliveries . It is believed that this is mostly due to the increasing caesarean section rate.
Key Diagnostic Signs
Ultrasound examination with colour Doppler and MRI scans may aid diagnosis.
First trimester: vascular lacunae may be seen within the placental mass.
Second and third trimesters: vascular lacunae which are long and thin rather than round (sensitivity 93% and a positive predictive value of 93%). Thinning or absence of the clear zone thought to be the decidua basalis, between the placenta and myometrium, and disruption of the posterior wall of the bladder are suggestive of abnormal invasion of placenta.
Colour flow Doppler ultrasonography may be performed in women with placenta praevia or low anterior placenta and a history of previous Caesarean section to diagnose abnormal invasion of placenta in the antenatal period. Diffuse lacunae with increased blood flow (peak systolic velocity >15 cm/seconds) and increased vascularity in the serosal-bladder interphase are suggestive of abnormal invasion of placenta (Figure 37.1).
The ‘smudged egg sign’ on the perioperative ultrasound scan
MRI is not essential if the diagnosis is suspected by an experienced sonographer but it may be useful in posterior placenta or when there is a suspicion of lateral extension into the broad ligament to establish the degree of extrauterine invasion.
Figure 37.1 Vascular lacunae and increased flow in the serosal/bladder interphase.
A dedicated multidisciplinary team: midwives, obstetricians, anaesthetist, interventional radiologists, hematologists and others (urologists and neonatologists).
Develop a local care bundle based on the recommendation by the National Patient Safety Agency (NPSA).
Blood and blood products should be made available at the time of surgery. Facilities for cell salvage (Figure 37.2) should be used if available . A clear multidisciplinary care plan should be made for women who refuse blood and blood products.
Figure 37.2 Cell saver.
Care should be tailored to the individual needs, including the desire to retain future fertility. The different risks and treatment options should be discussed and a plan agreed, including the anticipated skin and uterine incisions, tubal sterilisation or hysterectomy .
For women with placenta percreta, management options include conservative management of the placenta, elective caesarean hysterectomy with or without bladder resection or ureteric implantation or the ‘triple P procedure’. For women with suspected placenta accreta or increta, a range of conservative surgical options such as myometrial excision, multiple haemostatic sutures, uterine balloon tamponade or uterine compression sutures may be used.
All women who are at increased risk of massive obstetric haemorrhage (MOH) should be counselled regarding cell salvage and interventional radiology (prophylactic uterine artery balloon placement with or without pelvic arterial embolisation), the need for multiple blood transfusion, admission to intensive treatment unit, need for additional surgical procedures and emergency postpartum hysterectomy. Prevention and treatment of anaemia during the antenatal period should be optimised.
Women should be warned about the risks of iatrogenic preterm delivery.
If women are managed at home, they should be advised to attend immediately if they experience any bleeding, contractions or pain. Prolonged inpatient care is not required (except if there is evidence of placenta percreta and the threat of uterine rupture or perforation) and can be associated with an increased risk of thromboembolism.
If a woman is suspected of having placenta accrete, it is recommended that she is transferred to a unit with appropriate facilities (Figure 37.3).
Figure 37.3 Conservative management of placenta with fundal uterine incision.
Conservative Management: Leaving the Placenta In Situ
This should be considered when the preservation of fertility is desired or if placenta percreta has been diagnosed and invades vital structures. This may necessitate an extensive surgical procedure (e.g. peripartum hysterectomy with bladder resection, ureteric implantation) that may be associated with increased maternal morbidity and mortality.
An interventional radiologist should be involved in the care plan and preoperative prophylactic internal iliac balloon catheter placement should be considered. This will allow inflation of the occlusive balloons to reduce vascularity during surgery and therapeutic pelvic artery embolisation if massive obstetric hemorrhage occurs during surgery.
A midline incision should be considered, and the uterine incision should be preferably made in the uterine fundus to avoid incising the placenta. The fetus should be delivered through the uterine fundus and the umbilical cord clamped and ligated very close to the placental surface.
Oxytocics should be avoided if a decision is made to leave the entire placenta in situ because it may cause partial separation of the non-adherent placenta from the underlying myometrium, resulting is haemorrhage.
Patient should be prescribed antibiotics for 10 days post-surgery and inflammatory parameters should be carefully monitored. Serum beta human chorionic gonadotropin (β-hCG) measurement should be performed on the day of the surgery and weekly for 2 weeks.
Methotrexate should be not be considered because it has not shown any beneficial effect, with significant side effects .
Conservative management should be complicated by delayed haemorrhage or infection postoperatively that may necessitate a hysterectomy .
Coagulopathy due to a release of thromboplastins may also occur. Hence coagulation profile should be monitored weekly.