Guideline No. 402: Diagnosis and Management of Placenta Previa

Objectives: To summarize the current evidence and to make recommendations for diagnosis and classification of placenta previa and for managing the care of women with this diagnosis. Options: To manage in hospital or as an outpatient and to perform a cesarean delivery preterm or at term or to allow a trial of labour when a diagnosis of placenta previa or a low-lying placenta is suspected or confirmed. Outcomes: Prolonged hospitalization, preterm birth, rate of cesarean delivery, maternal morbidity and mortality, and postnatal morbidity and mortality. Intended Users: Family physicians, obstetricians, midwives, and other maternal care providers. Target Population: Pregnant women with placenta previa or low-lying placenta. Evidence: Medline, PubMed, Embase, and the Cochrane Library were searched from inception to October 2018. Medical Subject Heading (MeSH) terms and key words related to pregnancy, placenta previa, low-lying placenta, antepartum hemorrhage, short cervical length, preterm labour, and cesarean. This document represents an abstraction of the evidence rather than a methodological review. Validation Methods: This guideline has been reviewed by the Maternal-Fetal Medicine and Diagnostic Imaging committees of the Society of Obstetricians and Gynaecologists of Canada (SOGC) and approved by the SOGC Board of Directors. Benefits, Harms, and/or Costs: Women with placenta previa or low-lying placenta are at increased risk of maternal, fetal and postnatal adverse outcomes that include a potentially incorrect diagnosis and possibly unnecessary hospitalization, restriction of activities, early delivery, or cesarean delivery. Optimization of diagnosis and management protocols has potential to improve maternal, fetal and postnatal outcomes. SUMMARY STATEMENTS (GRADE ratings in parentheses): 1. All women with placenta previa or low-lying placenta have an increased risk of a morbidly adherent placenta, particularly those who have had a prior cesarean delivery (strong/moderate). 2. In women with placenta previa or a low-lying placenta, presence of a marginal/velamentous cord insertion close to the cervical os or a succenturiate placental lobe increases the risk of vasa previa (strong/moderate). 3. History of antepartum hemorrhage (first episode <29 weeks or recurrent episodes [>= 3]), a thick placental edge covering (or close to) the cervical os, short cervical length (<3 cm with placenta previa, <2 cm with low-lying placenta), and a previous cesarean delivery are risk factors with an associated increased risk of urgent/preterm cesarean delivery (strong/moderate). 4. In the absence of risk factors, outpatient management of women with placenta previa is safe (strong/moderate). 5. Bed rest or reduced activity is not beneficial in women with placenta previa and can be potentially harmful. However, sexual intercourse/ insertion of foreign bodies in vagina or rectum should be avoided (conditional [weak]/low). 6. Preoperative bedside ultrasound assessment of placental location can be useful for planning of surgical technique and may reduce risk of intraoperative transection of placenta (conditional [weak]/low). 7. Regional anaesthesia is safe and adequate as a first-line anaesthetic approach for the peripartum management of patients with placenta previa or low-lying placenta (conditional [weak]/low). 8. When deciding the location of delivery, consider ultrasound assessment of placental location, any risk factors, the patient's history, and logistical factors, including available resources at the delivery unit (conditional [weak]/low). RECOMMENDATIONS (GRADE ratings in parentheses): 1. Classify placental location as placenta previa (placenta covering the cervical os), low-lying placenta (edge located <= 20 mm from cervical os), or normally located placenta (edge located >20 mm from cervical os) (strong/moderate). 2. Diagnosis of placenta previa or low-lying placenta should not be made < 18 to 20 weeks gestation, and the provisional diagnosis must be confirmed after >32 weeks gestation, or earlier if the clinical situation warrants. In women with a low-lying placenta, a recent ultrasound (within 7 to 14 days) should be used to confirm placental location prior to a cesarean delivery (strong/moderate). 3. Assessment by transvaginal ultrasound is recommended in all cases where placenta previa or a low-lying placenta is present or suspected by transabdominal sonography, with attempt to clearly define placental location (including laterality), characteristics of placental edge (including thickness, presence of a marginal sinus), and associated findings (succenturiate lobe, cord insertion close to the cervix) (strong/moderate). 4. In women with placenta previa or low-lying placenta and in the presence of risk factors or limited access to urgent obstetrical care, consider in-hospital management (strong/moderate). 5. A cervical cerclage can be considered in women with a short cervical length, particularly in association with antepartum hemorrhage, but not as a prophylactic measure for all women with placenta previa (conditional [weak]/low). 6. Administer antenatal corticosteroids for potential preterm delivery only if the risk of delivery within 7 days is very high and not solely because admission to the hospital is deemed necessary (strong/ moderate). 7. Tocolysis can be considered in women with antepartum hemorrhage associated with uterine contractions in order to allow administration of corticosteroids or transfer of care, but not for prolongation of pregnancy (conditional [weak]/low). 8. Cesarean delivery is recommended in women with placenta previa at 360 to 366 weeks gestation in the presence of risk factors and at 370 to 376 weeks gestation in the absence of risk factors (strong/ moderate). 9. Cesarean delivery is recommended in women with a low-lying placenta with the placental edge <= 10 mm from the cervical os at 37(0) to 376 weeks gestation in the presence of risk factors and at 38(0) to 386 weeks gestation in the absence of risk factors (strong/ moderate). 10. A trial of labour is recommended in women with a low-lying placenta where the placental edge is 11 to 20 mm from the cervical os and can be considered in carefully selected women where the placental edge is <= 10 mm from the cervical os (strong/moderate).