BACKGROUND AND PURPOSE:

• Low-lying placenta is defined as an internal os distance (IOD) between 0-20 mm
• There are conflicting guidelines on the preferred mode of delivery
  • While there is a risk of bleeding and emergent cesarean delivery, some women will delivery vaginally
  • Benefit of cesarean section remains unproven
• Jansen et al. (BJOG, 2019) sought to determine the probability of a successful vaginal delivery with a low-lying placenta

METHODS:

• Systematic review and meta-analysis
  • Two independent reviewers
  • Eligible studies: (1) Vaginal delivery in patients with a low-lying placenta in the third trimester and/or (2) Morbidity related to mode of delivery in patients with a low-lying placenta in the third trimester was described
  • Prospective and retrospective cohort studies | Case-control studies | Case series with >10 cases | Conference abstracts with author contact
• Distinguished between IODs
  • >20 | 0–20 | 11–20 | 0–10 mm
• Primary outcome
  • proportion of women with a low-lying placenta and a successful vaginal delivery and no emergency cesarean due to hemorrhage
• Secondary outcomes
  • Maternal morbidity including
    • Antepartum and postpartum blood loss | Blood transfusion
  • Cesarean section rates due to hemorrhage

RESULTS:

• 10 articles included

• IOD of >20 mm: Statistically significant chance of successful vaginal delivery
  • Vaginal delivery success rate: 82% (95% CI 58–97)
  • Emergency cesarean rate (due to hemorrhage): 10% (95% CI 2.2–22.3)
  • Odds ratio (OR): 18.76 (95% CI 8.83–39.88; P < 0.01)
• IOD of 0–20: Not statistically different
  • Vaginal delivery success rate: 30% (95% CI 12–53)
  • Emergency cesarean rate: 38% (95% CI 27–50)
• IOD of 11–20 mm: Statistically significant chance of successful vaginal delivery
  • Vaginal delivery success rate: 85% (95% CI 70–96)
  • Emergency cesarean rate: 14% (95% CI 4.2–29)
  • OR: 9.90 (95% CI 5.78–16.96; P<0.01)
• IOD of 0–10 mm: Not statistically different
  • Vaginal delivery success rate: 43% (95% CI 28–59)
  • Emergency cesarean rate: 45% (95% CI 22–69)
• Shorter IOD had a higher chance of antepartum hemorrhage (3 studies)
• Larger IOD needed postpartum blood transfusion more often (one study)
• No relationship between IOD and risk of postpartum hemorrhage

CONCLUSION:

• Low-lying placenta does not require a cesarean section, although there is a higher risk of emergency cesarean section
• Even at 0 to 10mm, morbidity was not increased compared to >10mm
• The authors state

Therefore, women with a low-lying placenta having an IOD between 0 and 20 mm can have a trial of labour in a clinical setting after in-depth counselling and shared decision making

Learn More – Primary Sources:

Vaginal delivery in women with a low-lying placenta: a systematic review and meta-analysis

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