In addition to these evidence-based recommendations, the guideline development group also identifies points of best clinical practice in the original guideline document.
Classification of evidence levels (1+ to 4) and grades of recommendations (A-D) are defined at the end of the "Major Recommendations" field.
Screening and Diagnosis for Placenta Praevia/Accreta
Should We Screen for Placental Localisation?
D - Routine ultrasound scanning at 20 weeks of gestation should include placental localisation.
How Should We Image for Placental Localisation?
C - Transvaginal scans improve the accuracy of placental localisation and are safe, so the suspected diagnosis of placenta praevia at 20 weeks of gestation by abdominal scan should be confirmed by transvaginal scan.
Which Women Need Further Imaging if the Placenta Is Low at 20 Weeks of Gestation?
C - All women require follow-up imaging if the placenta covers or overlaps the cervical os at 20 weeks of gestation.
C - Women with a previous caesarean section require a higher index of suspicion as there are two problems to exclude: placenta praevia and placenta accreta. If the placenta lies anteriorly and reaches the cervical os at 20 weeks, a follow-up scan can help identify if it is implanted into the caesarean section scar.
When Should Further Imaging Occur?
D - In cases of asymptomatic women with suspected minor praevia, follow-up imaging can be left until 36 weeks of gestation.
D - In cases with asymptomatic suspected major placenta praevia or a question of placenta accreta, imaging should be performed at around 32 weeks of gestation to clarify the diagnosis and allow planning for third-trimester management, further imaging, and delivery.
How Can a Morbidly Adherent Placenta Be Diagnosed?
D - Antenatal sonographic imaging can be complemented by magnetic resonance imaging in equivocal cases to distinguish those women at special risk of placenta accreta.
Antenatal imaging techniques that can help to raise the suspicion of a morbidly adherent placenta should be considered in any situation where any part of the placenta lies under the previous caesarean section scar, but the definitive diagnosis can be made only at surgery. These techniques include ultrasound and magnetic resonance imaging.
Where Should Women with Placenta Praevia Be Cared for in the Late Third Trimester?
D - Any home-based care requires close proximity to the hospital, the constant presence of a companion, and full informed consent by the woman.
Is There a Place for Tocolytics in Women Who Bleed?
C - Tocolysis for treatment of bleeding due to placenta praevia may be useful in selected cases. However, beta-mimetics were used in the studies to date and, as these are known to be associated with significant adverse effects, the agent and optimum regime are still to be determined: further research is needed in this area.
Preparations for Delivery
In What Situations Can Vaginal Delivery Be Contemplated for Women with a Low-Lying Placenta?
C - The mode of delivery should be based on clinical judgement supplemented by sonographic information. A woman with a placental edge less than 2 cm from the internal os in the third trimester is likely to need delivery by caesarean section, especially if the placenta is thick, but the evidence for this is poor and further research in this area is needed.
At What Gestation Should Elective Delivery Occur?
D - Elective delivery by caesarean section in asymptomatic women is not recommended before 38 weeks of gestation for placenta praevia, or before 36–37 weeks of gestation for suspected placenta accreta.
What Blood Products Are Needed?
D - There is no evidence to support the use of autologous blood transfusion for placenta praevia.
D - Cell salvage may be considered in women at high risk of massive haemorrhage and especially in women who would refuse donor blood.
Suspected Placenta Accreta
D - Cross-matched blood and blood products should be readily available in anticipation of massive haemorrhage. Where available, cell salvage should be considered and if the woman refuses donor blood it is recommended that she be transferred to a unit with a cell saver.
When Is Interventional Radiology Indicated?
D - Interventional radiology can be life saving for the treatment of massive postpartum haemorrhage, and therefore having this facility available locally is desirable. If a woman is suspected of having placenta accreta and she refuses donor blood, it is recommended that she be transferred to a unit with an interventional radiology service.
D - The place of prophylactic catheter placement for balloon occlusion or in readiness for embolisation if bleeding ensues requires further evaluation.
What Grade of Obstetrician Should Attend?
D - Any woman going to theatre electively with suspected placenta praevia accreta should be attended by a consultant obstetrician and anaesthetist. If the delivery is unexpected, out-of-hours consultant staff should be alerted and attend as soon as possible.
Surgery in the Presence of Placenta Accreta, Increta, and Percreta
What Surgical Approach Should Be Used for Suspected Placenta Praevia Accreta?
C/D - Surgeons delivering the baby by caesarean section in the presence of a suspected placenta praevia accreta should consider opening the uterus at a site distant from the placenta, and delivering the baby without disturbing the placenta, in order to enable conservative management of the placenta or elective hysterectomy to be performed if the accreta is confirmed. Going straight through the placenta to achieve delivery is associated with more bleeding and a high chance of hysterectomy and should be avoided.
What Should Be Done if the Placenta Does Not Separate after Delivery of the Baby?
C/D - If the placenta fails to separate with the usual measures, leaving it in place and closing, or leaving it in place, closing the uterus and proceeding to a hysterectomy are both associated with less blood loss than trying to separate it.
What Happens if the Placenta Separates, or Partially Separates?
D - If the placenta partially separates, the separated portion(s) need to be delivered and any haemorrhage that occurs needs to be dealt with in the normal way. Adherent portions can be left in place, but blood loss in such circumstances can be large and massive haemorrhage management needs to follow in a timely fashion.
How Is Massive Haemorrhage Best Managed?
D - The surgical manoeuvres required in the face of massive haemorrhage associated with placenta praevia caesarean sections should be performed by appropriately experienced surgeons. Calling for extra help early should be encouraged and not seen as 'losing face'.
Management of massive haemorrhage should occur in the normal way, including the use of uterotonic agents, which can be very helpful in reducing the blood loss associated with bleeding from the relatively atonic lower uterine segment. Advanced techniques may also be employed and the use of bimanual compression or even aortic compression can buy time for extra help to arrive, or for the anaesthetist to 'catch up' haemodynamically in the unstable woman. [Evidence level 3]
Follow-Up of the Woman after Part or All of the Placenta Has Been Retained Following Placenta Accreta
How Should the Woman Be Managed after Placental Retention?
D - The woman should be warned of the risks of bleeding and infection postoperatively and prophylactic antibiotics may be helpful in the immediate postpartum period to reduce this risk. Neither methotrexate nor arterial embolisation reduces these risks and neither is recommended routinely.
Can We Diagnose Vasa Praevia Clinically?
In the antenatal period, in the absence of vaginal bleeding, there is no method to diagnose vasa praevia clinically.
D - In the intrapartum period, in the absence of vaginal bleeding, vasa praevia can occasionally be diagnosed clinically by palpation of fetal vessels in the membranes at the time of vaginal examination. This can be confirmed by direct visualisation using an amnioscope.
Without access to the fetal membranes, it is not possible to diagnose the intact vessels of vasa praevia clinically. Once the cervix has started to dilate, these vessels may be felt digitally during a vaginal examination. As the condition is rare, most clinicians will not be familiar with what they are feeling, and it is therefore important for clinicians to have a high index of suspicion if they feel something unusual and to confirm the diagnosis prior to membrane rupture if the consequences of fetal haemorrhage are to be avoided. Direct visualisation using an amnioscope has some use, but this only gives visual access to the area of membranes exposed by the dilated cervix. [Evidence level 3]
Following delivery of the placenta, it is easy to confirm the presence of fetal vessels running through the membranes by simple clinical examination, but it is more difficult to diagnose vasa praevia as the orientation of the vessels in relation to the internal cervical os and fetal presenting part in utero is not certain after delivery.
D - In the presence of vaginal bleeding, especially associated with membrane rupture and fetal compromise, delivery should not be delayed to try and diagnose vasa praevia.
Because of the speed at which fetal exsanguination can occur and the high perinatal mortality rate associated with ruptured vasa praevia, delivery should not be delayed while trying to confirm the diagnosis if fetal wellbeing is compromised. [Evidence level 4]
Can We Differentiate between Fetal and Maternal Bleeding?
C - Various tests exist that can differentiate between fetal and maternal blood, but they are often not applicable in the clinical situation.
Can Vasa Praevia Be Diagnosed Using Ultrasound?
C - Vasa praevia can be accurately diagnosed with colour Doppler ultrasound, often utilising the transvaginal route.
Should We Screen for Vasa Praevia?
D - At present, vasa praevia should not be screened for routinely at the time of the mid-trimester anomaly scan, as it does not fulfill the criteria for a screening programme.
How Should Vasa Praevia Be Managed?
C - In the presence of bleeding vasa praevia, delivery should be achieved by category 1 emergency caesarean section.
Fetal wellbeing should be confirmed at the time of any antepartum or intrapartum haemorrhage, and this is currently best achieved using the cardiotocograph. If signs of acute fetal compromise are present, delivery should be achieved as soon as possible, usually by category 1 caesarean section, to minimise the risk of fetal exsanguination. Delay to facilitate ultrasound or transfer to another unit could result in fetal demise. [Evidence level 2+]
C - In cases of suspected vasa praevia, transvaginal colour Doppler ultrasonography should be carried out to confirm the diagnosis.
If there is either an ultrasound or clinical suspicion of vasa praevia in the absence of fetal compromise, a formal systematic assessment of the region of the internal cervical os should be undertaken using transvaginal colour Doppler ultrasound. [Evidence level 2+]
C - In confirmed cases of vasa praevia at term, delivery should be carried out by elective caesarean section in a timely manner.
In view of the risk of fetal haemorrhage with the onset of labour or membrane rupture and the minimal risks of neonatal lung disease, once vasa praevia has been confirmed at term, delivery should be carried out by elective caesarean section as soon as is practicable. [Evidence level 2+]
D - In cases of confirmed vasa praevia in the third trimester, antenatal admission from 28 to 32 weeks of gestation to a unit with appropriate neonatal facilities will facilitate quicker intervention in the event of bleeding or labour.
A - In view of the increased risk of preterm delivery, administration of corticosteroids for fetal lung maturity should be considered.
C - In the presence of confirmed vasa praevia, elective caesarean section should be carried out prior to the onset of labour.
D - Laser ablation in utero may have a role in the treatment of vasa praevia.
Grades of Recommendations
A - At least one meta-analysis, systematic review or randomised controlled trial rated as 1++ and directly applicable to the target population; or
A systematic review of randomised controlled trials or a body of evidence consisting principally of studies rated as 1+ directly applicable to the target population and demonstrating overall consistency of results
B - A body of evidence including studies rated as 2++ directly applicable to the target population, and demonstrating overall consistency of results; or
Extrapolated evidence from studies rated as 1++ or 1+
C - A body of evidence including studies rated as 2+ directly applicable to the target population and demonstrating overall consistency of results; or
Extrapolated evidence from studies rated as 2++
D - Evidence level 3 or 4; or
Extrapolated evidence from studies rated as 2+
Good Practice Point - Recommended best practice based on the clinical experience of the guideline development group
Classification of Evidence Levels
1++ High-quality meta-analyses, systematic reviews of randomised controlled trials, or randomised controlled trials with a very low risk of bias
1+ Well-conducted meta-analyses, systematic reviews of randomised controlled trials, or randomised controlled trials with a low risk of bias
1– Meta-analyses, systematic reviews of randomised controlled trials, or randomised controlled trials with a high risk of bias
2++ High-quality systematic reviews of case–control or cohort studies or high-quality case–control or cohort studies with a very low risk of confounding, bias, or chance and a high probability that the relationship is causal
2+ Well-conducted case–control or cohort studies with a low risk of confounding, bias, or chance and a moderate probability that the relationship is causal
2– Case–control or cohort studies with a high risk of confounding, bias, or chance and a significant risk that the relationship is not causal
3 Non-analytical studies; e.g., case reports, case series
4 Expert opinion