Placenta Previa: Diagnosis and Management
Definition and Epidemiology
- Placenta previa occurs in approximately 1 in 200 pregnancies at delivery, characterized by abnormal placental placement that obstructs the cervical opening 1, 2
Risk Factors
- Prior cesarean delivery is the most significant risk factor, with risk increasing dramatically with each subsequent cesarean section, from 3% with placenta previa and no prior cesarean to 11%, 40%, 61%, and 67% for first, second, third, fourth, and fifth or more cesareans respectively 3
- Advanced maternal age is a risk factor for placenta previa 3
Diagnosis
- Transvaginal ultrasound is the gold standard diagnostic modality with sensitivity of 90.7% and specificity of 96.9% 2
- Digital pelvic examination must be avoided until placenta previa has been excluded to prevent triggering catastrophic hemorrhage 1, 2, 5
Management
- Women with asymptomatic placenta previa before 28 weeks can continue moderate-to-vigorous physical activity, but after 28 weeks should restrict activity to low-intensity walking and activities of daily living 2, 4
- Planned cesarean delivery at 34 0/7 to 35 6/7 weeks gestation is recommended for uncomplicated placenta previa to balance neonatal morbidity against maternal hemorrhage risk 2
- Delivery must not be delayed beyond 36 0/7 weeks as approximately 50% of women with placenta accreta spectrum beyond 36 weeks require emergent delivery for hemorrhage 2, 4
Intraoperative Management
- The surgical approach involves careful planning with uterine incision placed away from the placenta when possible, and if placenta accreta spectrum is encountered, the placenta must be left in situ 2
- Forced placental removal must be avoided as it causes profuse hemorrhage 2, 4
Massive Hemorrhage Protocol
- When transfusing for acute hemorrhage, use a fixed ratio of 1:1:1 to 1:2:4 for packed red blood cells:fresh frozen plasma:platelets 2, 5