The SWPSN offers monthly MDTs for the following specialties:
The meetings are co-chaired by a medical specialist with expertise in pregnancy care and an obstetrician with expertise in maternal medicine as well as an obstetric anaesthetist where needed.
These interesting meetings are of great educational value and we encourage attendance by all clinicians who may care for pregnant women as part of their work.
To be added to the invite list please email PASteam@nbt.nhs.uk from an nhs email address and let us know which of the MDT invitations you would like to receive.
Executive Summary
Placenta praevia and placenta accreta spectrum (PAS) are serious obstetric conditions associated with significant maternal and neonatal morbidity and mortality.
For pregnancies beyond 16 weeks of gestation, placental location should be reported as:
- “Low-lying” if the placental edge is <20 mm from the internal os.
- “Normal” if the placental edge is ≥20 mm from the internal os (assessed via transabdominal or transvaginal ultrasound).
The estimated incidence of placenta praevia at term is 1 in 200 pregnancies, while placenta accreta occurs in 1 in 300 to 1 in 2000 pregnancies. Rising rates of caesarean deliveries, advanced maternal age, and assisted reproductive technology (ART) have contributed to increased prevalence, placing greater demands on maternity resources (RCOG, 2018).
Definitions
Placenta praevia: The placenta lies directly over the internal os.
Placenta accreta spectrum (PAS): A histopathological diagnosis ranging from abnormal adherence to deep invasion of placental tissue. Cases may be classified as total, partial, or focal, and different invasion depths (e.g., accreta, increta, percreta) can coexist.
1.0 Roles and Responsibilities
- Doctors: Diagnosis and clinical management.
- Sonographers: Perform scans in accordance with guidelines.
- Midwives: Review ultrasound results, facilitate consultant referrals, and provide inpatient care within their scope.
2.0 Implementation and Dissemination
This guideline is available on the Trust Intranet. Printed copies are uncontrolled; always refer to the Intranet for the latest version.
3.0 Processes and Procedures
3.1 Risk Factors
- Key risk factors include:
- Advanced maternal age
- Multiparity
- Prior caesarean sections (risk escalates with each subsequent CS)
- History of placenta praevia
- Smoking
- ART (e.g., IVF)
- Multiple pregnancy
- Previous uterine surgery (e.g., D&C)
3.2 Grading Placenta Praevia and Accreta
- Normal placental location: ≥20 mm from the internal os on transvaginal ultrasound (TVS).
- PAS subtypes:
- Accreta (adherenta): Villi attach superficially to the myometrium.
- Increta: Villi invade deeply into the myometrium.
- Percreta: Villi penetrate the uterine wall, potentially involving adjacent organs (e.g., bladder).
3.3 Identification
- Definitive diagnosis: Ultrasound imaging.
- Clinical suspicion: Consider in patients with vaginal bleeding, high presenting part, or abnormal fetal lie, regardless of prior imaging results.
- Routine anomaly scan: Should include placental localization to identify at-risk pregnancies (RCOG, 2018).
3.4 Recommendations for Ultrasound Follow-Up
- TVS is superior to transabdominal or transperineal scans for diagnosing placenta praevia/low-lying placenta (RCOG, 2018).
- Anterior low-lying placenta/praevia in scarred uterus: Rescan at 28 weeks. If persistent, refer to fetal medicine for PAS evaluation.
- Asymptomatic patients with persistent low-lying placenta/praevia at 32 weeks: Repeat TVS at 36 weeks to guide delivery planning.
- Delivery planning:
- Elective CS at 37 weeks if placenta remains low-lying at 32 weeks.
- If the placenta migrates by 36 weeks, aim for normal vaginal delivery (NVD) or reschedule CS to 39 weeks if other indications persist.
- Cervical length measurement: A short cervix (<34 weeks) predicts higher risk of preterm delivery and hemorrhage.
