Placenta Previa Grading and Management
Placenta previa should be classified based on the relationship between the placental edge and the internal cervical os, with management strategies tailored to each type to reduce maternal morbidity and mortality. 1
Classification of Placenta Previa
- Complete placenta previa: Placental tissue completely covers the internal cervical os 2, 1
- Partial placenta previa: Placental tissue partially covers the internal cervical os 1
- Marginal placenta previa: Placental edge reaches the internal cervical os but does not cover it 1
- Low-lying placenta: Placental edge is within 2 cm of the internal cervical os but does not reach it 3
Diagnostic Approach
- Transvaginal ultrasound is the gold standard for diagnosing and classifying placenta previa with high sensitivity (90.7%) and specificity (96.9%) 2, 1
- Transabdominal ultrasound should be performed initially, followed by transvaginal ultrasound for more accurate assessment 2
- Doppler ultrasound is essential to identify vasa previa and assess placental blood flow patterns 2
- Digital pelvic examination must be avoided until placenta previa is excluded to prevent triggering hemorrhage 1, 4
Risk Assessment
- Prior cesarean delivery significantly increases risk of placenta previa and placenta accreta spectrum (PAS) 1, 4
- Risk of PAS increases 7-fold after one cesarean and up to 56-fold after three cesarean deliveries 1
- Additional risk factors: advanced maternal age, multiparity, prior uterine surgery, smoking, and multifetal gestation 4
- Women with one bleeding episode are at increased risk for subsequent bleeding 1
Management Based on Classification
Complete or Partial Placenta Previa
- Delivery method: Cesarean delivery is mandatory 1, 4
- Timing: 34 0/7-35 6/7 weeks of gestation in stable patients 1
- Earlier delivery indicated for persistent bleeding, preeclampsia, labor, rupture of membranes, or fetal compromise 1
- Antenatal corticosteroids should be administered when delivery is anticipated before 37 weeks 1
Marginal Placenta Previa
- Delivery method: Usually requires cesarean delivery, especially if the placental edge overlaps or is within 2 cm of the internal os 3
- Timing: Similar to complete previa if cesarean is planned 1
Low-lying Placenta (>2 cm from internal os)
- Delivery method: Vaginal delivery may be attempted 3
- Caution: Higher risk of postpartum hemorrhage even with successful vaginal delivery 3
Activity Recommendations
- Before 28 weeks: Women with asymptomatic placenta previa can continue moderate physical activity 1
- After 28 weeks: Avoid moderate-to-vigorous physical activity but maintain activities of daily living 1
- Hospitalization recommended for women with active bleeding 1, 5
Preoperative Planning for Cesarean Delivery
- Delivery should occur at a facility with adequate blood banking and multidisciplinary expertise 1, 4
- Coordinate with anesthesiology, maternal-fetal medicine, neonatology, and expert pelvic surgeons 1
- Optimize hemoglobin values during pregnancy; treat anemia with iron supplementation 1
- Notify blood bank in advance due to frequent need for large-volume transfusion 1
Intraoperative Management
- Consider dorsal lithotomy positioning to allow access to vagina and optimal surgical visualization 1
- Make uterine incision away from the placenta when possible 1
- If abnormal placental attachment is found, leave the placenta in situ; forced removal can cause massive hemorrhage 1, 6
- In cases of PAS, cesarean hysterectomy may be necessary 1, 2
Special Considerations for Placenta Accreta Spectrum
- Evaluate all women with placenta previa and prior cesarean deliveries for PAS 2, 1
- MRI may be helpful in difficult cases such as posterior placenta previa or suspected placenta percreta 2
- For suspected bladder involvement, consider ureteric stent placement and urologic consultation 1
- In cases of hemorrhage, use a 1:1:1 to 1:2:4 ratio of packed red blood cells:fresh frozen plasma:platelets 2, 1
Follow-up Care
- Ensure adequate iron supplementation and monitor hemoglobin levels if significant blood loss occurred 1
- Intensive hemodynamic monitoring in the early postoperative period, especially after significant hemorrhage 1
- Maintain vigilance for ongoing bleeding with low threshold for reoperation if suspected 1