Placental Abnormalities (Topic Discussion)

Antenatal diagnosis and care of women with placenta praevia or a low-lying placenta

What are the risk factors for women with placenta praevia or a low-lying placenta?

1)-Caesarean delivery is associated with an increased risk of placenta praevia in subsequent pregnancies. This risk rises as the number of prior caesarean sections increases. 

2)- Assisted reproductive technology and

3)- Maternal smoking increase the risk of placenta praevia.

Should we screen women for placenta praevia or a low-lying placenta, if so, at what gestation and with what follow-up?

The midpregnancy routine fetal anomaly scan should include placental localisation thereby identifying women at risk of persisting placenta praevia or a low-lying placenta. 

Define Placenta Previa 

The term placenta praevia should be used when the placenta lies directly over the internal os.

For pregnancies at more than 16 weeks of gestation the term low-lying placenta should be used when the placental edge is less than 20 mm from the internal os on transabdominal or

transvaginal scanning (TVS). 

If the placenta is thought to be low lying (less than 20 mm from the internal os) or praevia (covering the os) at the routine fetal anomaly scan, a follow-up ultrasound examination

including a TVS is recommended at 32 weeks of gestation to diagnose persistent low-lying placenta and/or placenta praevia. 

What is the role and what are the risks of TVS?

Clinicians should be aware that TVS for the diagnosis of placenta praevia or a low-lying placenta is superior to transabdominal and transperineal approaches, and is safe. 

In women with a persistent low-lying placenta or placenta praevia at 32 weeks of gestation who remain asymptomatic, an additional TVS is recommended at around 36 weeks of gestation to inform discussion about mode of delivery. 

What is the role of Cervical length Measurement ?

Cervical length measurement may help facilitate management decisions in asymptomatic women with placenta praevia. 

A short cervical length on TVS before 34 weeks of gestation increases the risk of preterm emergency delivery and massive haemorrhage at caesarean section. 

Where should women with a low-lying placenta or placenta praevia be cared for in the third trimester?

In women with recurrent bleeding (low-lying placenta or placenta praevia) tailor antenatal care, including hospitalisation, to individual woman’s needs and social

circumstances, e.g. distance between home and hospital and availability of transportation, previous bleeding episodes, haematology laboratory results, and acceptance of receiving donor blood or blood products. 

This will need to balance the risk of developing a venous thromboembolism against the risk of bleeding from a placenta praevia or low lying placenta.

It should be made clear to any woman being treated at home in the third trimester that she should attend the hospital immediately if she experiences any bleeding, including spotting, contractions or pain (including vague suprapubic period-like aches).

Asymptomatic women (low-lying placenta or placenta praevia)

Women with asymptomatic placenta praevia or a low-lying placenta in the third trimester should be counselled about the risks of preterm delivery and obstetric haemorrhage, and their

care should be tailored to their individual needs.

Women with asymptomatic placenta praevia confirmed at the 32-week follow-up scan and managed at home should be encouraged to ensure they have safety precautions in place,

including having someone available to help them as necessary and ready access to the hospital.

Is there a place for cervical cerclage in women with placenta praevia or a low-lying placenta?

The use of cervical cerclage to reduce bleeding and prolong pregnancy is not supported by sufficient evidence to recommend its use outside of a clinical trial.

In what circumstances, and at what gestation, should women be offered antenatal corticosteroids?

A single course of antenatal corticosteroid therapy is recommended between 34+0 and 35+6 weeks of gestation for pregnant women with a low-lying placenta or placenta praevia and is appropriate prior to 34+0 weeks of gestation in women at higher risk of preterm birth.

Is there a place for the use of tocolytics in women presenting with symptomatic low-lying placenta or placenta

praevia, who are in suspected preterm labour?

Tocolysis for women presenting with symptomatic placenta praevia or a low-lying placenta may be considered for 48 hours to facilitate administration of antenatal corticosteroids. 

If delivery is indicated based on maternal or fetal concerns, tocolysis should not be used in an attempt to prolong gestation. 

At what gestation should planned delivery occur?

Late preterm (34+0 to 36+6 weeks of gestation) delivery should be considered for women presenting with placenta praevia or a low-lying placenta and a history of vaginal bleeding or other associated risk factors for preterm delivery. 

Delivery timing should be tailored according to antenatal symptoms and, for women presenting with uncomplicated placenta praevia, delivery should be considered between 36+0 and 37+0 weeks of gestation. 

In what situations is vaginal delivery appropriate for women with a low-lying placenta?

In women with a third trimester asymptomatic low-lying placenta the mode of delivery should be based on the clinical background, the woman’s preferences, and supplemented by

ultrasound findings, including the distance between the placental edge and the fetal head position relative to the leading edge of the placenta on TVS. 

Optimising the delivery of women with placenta praevia

Prior to delivery, all women with placenta praevia and their partners should have a discussion regarding delivery. 

Indications for blood transfusion and hysterectomy should be reviewed and any plans to decline blood or blood products should be discussed openly and documented.

Placenta praevia and anterior low-lying placenta carry a higher risk of massive obstetric haemorrhage and hysterectomy. 

Delivery should be arranged in a maternity unit with on-site

blood transfusion services and access to critical care.

Women with atypical antibodies form a particularly high-risk group and the care of these women should involve discussions with the local haematologist and blood bank. 

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

Delivery for women with placenta praevia or a low-lying placenta

What grade of obstetrician and anaesthetist should attend the caesarean delivery of a woman with placenta praevia?

As a minimum requirement for a planned caesarean section for a woman with placenta praevia, the surgical procedure should be carried out by an appropriately experienced operator.

In cases of planned caesarean section for placenta praevia or a low-lying placenta, a senior obstetrician (usually a consultant) and senior anaesthetist (usually a consultant) should be present within the delivery or theatre suite where the surgery is occurring.

When an emergency arises, the senior obstetrician and senior anaesthetist should be alerted immediately and attend urgently.

What anaesthetic procedure is most appropriate for women having a caesarean section for placenta praevia?

Regional anaesthesia is considered safe and is associated with lower risks of haemorrhage than general anaesthesia for caesarean delivery in women with placenta praevia or a low-lying placenta. Women with anterior placenta praevia or a low-lying placenta should be advised that it

may be necessary to convert to general anaesthesia if required and asked to consent. 

What blood products should be available?

Close liaison with the hospital transfusion laboratory is essential for women presenting with placenta praevia or a low-lying placenta. 

Rapid infusion and fluid warming devices should be immediately available.

Cell salvage is recommended for women where the anticipated blood loss is great enough to induce anaemia, in particular, in women who would decline blood products. 

What surgical approach should be used for women with placenta praevia or a low-lying placenta?

1)-Consider vertical skin and/or uterine incisions when the fetus is in a transverse lie to avoid the placenta, particularly below 28 weeks of gestation. 

2)-Consider using preoperative and/or intraoperative ultrasonography to precisely determine placental location and the optimal place for uterine incision. 

3)-If the placenta is transected during the uterine incision, immediately clamp the umbilical cord after fetal delivery to avoid excessive fetal blood loss.

4)-If pharmacological measures fail to control haemorrhage, initiate intrauterine tamponade and/or surgical haemostatic techniques sooner rather than later. Interventional radiological techniques should also be urgently employed where possible. 

5)-Early recourse to hysterectomy is recommended if conservative medical and surgical interventions prove ineffective. 

Antenatal diagnosis and outcome of women with placenta accreta spectrum

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

The major risk factors for placenta accreta spectrum are 

1)-History of accreta in a previous pregnancy, 

2)-Previous caesarean delivery and other uterine surgery, including repeated endometrial curettage. This risk rises as the number of prior caesarean sections increases. 

3)-Previous history of Placenta previa 

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.

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. 

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. 

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. 

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

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. 

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. 

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.

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.

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 neonatal intensive care unit by a multidisciplinary team with expertise in complex pelvic surgery. 

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. 

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. 

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.

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

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.

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.

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. 

Optimising the delivery of women with placenta accreta spectrum

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

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

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. 

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. 

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 .

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. 

Expectant management (leaving the placenta in situ)

Elective peripartum hysterectomy may be unacceptable to women desiring uterine preservation

or considered inappropriate by the surgical team. In such cases, leaving the placenta in situ

should be considered. 

When the placenta is left in situ, local arrangements need to be made to ensure regular review, ultrasound examination and access to emergency care should the woman experience

complications, such as bleeding or infection. 

Methotrexate adjuvant therapy should not be used for expectant management as it is of unproven benefit and has significant adverse effects. 

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.

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

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. 

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. 

VASA PRAEVIA

Management of women with undiagnosed vasa praevia at delivery. Emergency caesarean delivery and neonatal resuscitation, including the use of blood transfusion

if required, are essential in the management of ruptured vasa praevia diagnosed during labour. 

Placental pathological examination should be performed to confirm the diagnosis of vasa praevia, in particular when stillbirth has occurred or where there has been acute fetal

compromise during delivery. 

Can vasa praevia be diagnosed antenatally?

The performance of ultrasound in diagnosing vasa praevia at the time of the routine fetal anomaly scan has a high diagnostic accuracy with a low false-positive rate. 

A combination of both transabdominal and transvaginal colour Doppler imaging (CDI) ultrasonography provides the best diagnostic accuracy for vasa praevia.

Should we screen for vasa praevia?

There is insufficient evidence to support universal screening for vasa praevia at the time of the routine midpregnancy fetal anomaly scan in the general population. 

Although targeted midpregnancy ultrasound screening of pregnancies at higher risk of vasa praevia may reduce perinatal loss, the balance of benefit versus harm remains undetermined and further research in this area is required. 

How should women with vasa praevia be managed?

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, particularly if there is evidence that fetal wellbeing is compromised. 

In the presence of confirmed vasa praevia in the third trimester, elective caesarean section should ideally be carried out prior to the onset of labour.

A decision for prophylactic hospitalisation from 30–32 weeks of gestation in women with confirmed vasa praevia should be individualised and based on a combination of factors,

including multiple pregnancy, antenatal bleeding and threatened premature labour. 

In cases of vasa praevia that develop premature rupture of membranes and/or labour at viable gestational ages, a caesarean section should be performed without delay. 

To avoid unnecessary anxiety, admissions, prematurity and caesarean section, it is essential to confirm persistence of vasa praevia by ultrasound in the third trimester.

At what gestation should elective delivery occur?

The ultimate management goal of confirmed vasa praevia should be to deliver before rupture of membranes while minimising the impact of iatrogenic prematurity. 

Based on available data, planned caesarean delivery for a prenatal diagnosis of vasa praevia at 34–36 weeks of gestation is reasonable in asymptomatic women. 

Administration of corticosteroids for fetal lung maturity should be recommended from 32 weeks of gestation due to the increased risk of preterm delivery.