BACKGROUND AND PURPOSE: 

• There is concern that a prolonged second stage of labor may result in injury to the cervix, leading to subsequent preterm birth  
• Quiñones et al. (AJOG 2018) analyzed whether the length of the second stage of labor in a first delivery is associated with an increased risk of preterm delivery

METHODS: 

• Retrospective cohort study 
  • 2 consecutive pregnancies 
  • First delivery: Term (≥37 weeks), nulliparous  
  • Subsequent second birth: Delivery >16w0d 
• Exposure: Second-stage duration, defined as time from complete dilation to delivery   
  • Short: <30 minutes 
  • Normal: 0–179 minutes 
  • Prolonged: ≥180 minutes 
• Primary outcome: Spontaneous preterm delivery in the second pregnancy 
• 90% power to detect a 1.5-fold increased risk of spontaneous preterm delivery with a prolonged second stage ≥180 minutes in the first pregnancy 

RESULTS: 

• 6715 women were included 
  • Short duration: 26.0% 
  • Normal duration: 67.8% 
  • Prolonged duration: 6.2% 
• Prolonged labor was associated with greater risk of spontaneous preterm delivery 
  • Prolonged second stage: 5.4% 
  • Normal labor duration: 3.5%  
  • Adjusted hazard ratio (HR) 1.81 (95% confidence interval, 1.15–2.84) 
• This increased risk associated with prolonged second stage was mostly seen in women who underwent a cesarean 
  • HR 3.38 (95% CI, 1.09–10.49)  
  • Not significant for vaginal delivery (HR 1.52; 95% CI, 0.62–3.74) 
• Short second stage of labor was also associated with increased risk for preterm delivery but with ‘borderline’ significance  
  • HR 1.28 (95% CI, 0.99–1.67)

CONCLUSION: 

• Prolonged second stage in first term pregnancy was associated with a higher risk of spontaneous preterm delivery 
• This risk was even greater among women who were delivered by cesarean in the first pregnancy 
• The authors state 

There may be unintended consequences of prolonging a second stage of labor ≥3 hours for nulliparous women with respect to the outcome of the next pregnancy, particularly in women who undergo a cesarean after a prolonged second stage of labor.

Learn More – Primary Sources: 

Length of the second stage of labor and preterm delivery risk in the subsequent pregnancy

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