In addition to these evidence-based recommendations, the guideline development group also identifies points of best clinical practice in the original guideline document.
Levels of evidence (Ia-IV) and grading of recommendations (A-C) are defined at the end of the "Major Recommendations" field.
Screening and Diagnosis
While clinical acumen remains vitally important in suspecting and managing placenta praevia, the definitive diagnoses of most low-lying placentas is now achieved with ultrasound imaging. Clinical suspicion should, however, be raised in any woman with vaginal bleeding and a high presenting part or an abnormal lie, irrespective of previous imaging results.
Ultrasound Imaging in Screening for Low-Lying Placenta and Diagnosing Placenta Praevia
B - Transvaginal ultrasound is safe in the presence of placenta praevia and is more accurate than transabdominal ultrasound in locating the placenta.
C - A reasonable antenatal imaging policy is to perform a transvaginal ultrasound scan on all women in whom a low-lying placenta is suspected from their transabdominal anomaly scan (at approximately 20-24 weeks) to reduce the numbers of those for whom follow-up will be needed.
C - A further transvaginal scan is required for all women whose placenta reaches or overlaps the cervical os at their anomaly scan as follows:
- Women who bleed should be managed individually according to their needs.
- In cases of asymptomatic suspected minor praevia, follow-up imaging can be left until 36 weeks.
- In cases with asymptomatic suspected major placenta praevia, a transvaginal ultrasound scan should be performed at 32 weeks, to clarify the diagnosis and allow planning for third-trimester management and delivery.
Diagnosis of a Morbidly Adherent Placenta
C - Antenatal imaging by colour flow Doppler ultrasonography should be performed in women with placenta praevia who are at increased risk of placenta accreta. Where this is not possible locally, such women should be managed as if they have placenta accreta until proven otherwise.
Women with placenta praevia are at increased risk of having a morbidly adherent placenta if they have an anterior placenta praevia and have previously been delivered by caesarean section, especially when there has been a short caesarean to conception interval. Antenatal imaging can help to establish a diagnosis in such cases and techniques used include ultrasound imaging, power amplitude ultrasonic angiography, magnetic resonance imaging (MRI), and colour flow Doppler.
Imaging antenatally allows for preparation for surgery but false positives do occur and the diagnosis should be confirmed intraoperatively to avoid inappropriate treatment.
Antenatal Management
C - Women with major placenta praevia who have previously bled should be admitted and managed as inpatients from 34 weeks of gestation. Those with major placenta praevia who remain asymptomatic, having never bled, require careful counselling before contemplating outpatient care. Any home-based care requires close proximity with the hospital, the constant presence of a companion, and full informed consent from the woman.
Delivery
B - The mode of delivery should be based on clinical judgement supplemented by sonographic information. A placental edge less than 2 cm from the internal os is likely to need delivery by caesarean section, especially if it is posterior or thick.
B - There is no evidence to support the use of autologous blood transfusion for placenta praevia.
C - Cell salvage may be considered in cases at high risk of massive haemorrhage.
B - The choice of anaesthetic technique for caesarean section for placenta praevia must be made by the anaesthetist, in consultation with the obstetrician and mother, but there is increasing evidence to support the safety of regional blockade.
Surgery in the Presence of Placenta Accreta, Increta, and Percreta
C - Women with placenta praevia who have had a previous caesarean section are at high risk of having a morbidly adherent placenta and should have been imaged antenatally. When placenta accreta is thought to be likely, consultant anaesthetic and obstetric input are vital in planning and conducting the delivery. Crossed matched blood should be available and colleagues from other specialties/subspecialties may be alerted to be on standby to attend as needed.
B - Conservative management of placenta praevia accreta can be successful and can preserve fertility. This can involve a number of different management strategies, which are outlined in the original guideline document, but precise recommendations are outside the scope of this guideline.
Massive Haemorrhage
C - Massive haemorrhage should be dealt with in accordance with the recommendations of the reports of the Confidential Enquiries into Maternal Deaths.
Uterotonic agents may help in reducing the blood loss associated with bleeding from the relatively atonic lower uterine segment, while bimanual compression, hydrostatic balloon catheterization, or uterine packing, or even aortic compression, can buy time while senior help arrives. Additional surgical manoeuvres which may be considered include the B-Lynch suture, uterine or internal iliac artery ligation, or hysterectomy. Arterial embolisation has been reported and is useful in selected cases as long as the iliac vessels have not been tied off.
Risk Management
As in all high-risk cases, particular attention should be paid to careful documentation of all issues surrounding clinical discussion and decisions. Names of all clinical staff involved should be recorded legibly and signed in the notes, together with the content of any discussions, advanced directives, and decisions.
Definitions:
Grading of Recommendations
Grade A - Requires at least one randomised controlled trial as part of a body of literature of overall good quality and consistency addressing the specific recommendation (evidence levels Ia, Ib)
Grade B - Requires the availability of well-conducted clinical studies but no randomised clinical trials on the topic of recommendations (evidence levels IIa, IIb, III)
Grade C - Requires evidence obtained from expert committee reports or opinions and/or clinical experience of respected authorities. Indicates an absence of directly applicable clinical studies of good quality (evidence level IV)
Levels of Evidence
Ia: Evidence obtained from meta-analysis of randomised controlled trials
Ib: Evidence obtained from at least one randomised controlled trial
IIa: Evidence obtained from at least one well-designed controlled study without randomisation
IIb: Evidence obtained from at least one other type of well-designed quasi-experimental study
III: Evidence obtained from well-designed non-experimental descriptive studies, such as comparative studies, correlation studies, and case studies
IV: Evidence obtained from expert committee reports or opinions and/or clinical experience of respected authorities
