Grand Rounds

Secondary Analysis of ARRIVE RCT: The Association Between Amniotomy During Induction and Cesarean Delivery

BACKGROUND AND PURPOSE:

Early amniotomy during induction likely decreases the duration of labor
- Effect on cesarean delivery is less well understood
Battarbee et al. (American Journal of Perinatology, 2020) assessed the association between amniotomy in nulliparous women and risk for cesarean delivery

Secondary analysis of the ARRIVE RCT (NICHD/MFMU)
- Purpose of original study was to assess perinatal outcomes in nulliparous women randomized to elective induction at 39 weeks vs expectant management
Participants (inclusion criteria)
- Low-risk, nulliparous women
- Induction ≥38 weeks using oxytocin
- Excluded were women with antepartum stillbirth or fetal anomaly
Study design
- The authors compared outcomes between
  - Women with amniotomy
  - Women with intact membranes and no amniotomy
- Comparisons were performed at six 2-hour time intervals
  - Before oxytocin initiation
  - 0 to <2 hours after oxytocin
  - 2 to <4 hours after
  - 4 to <6 hours after
  - 6 to <8 hours after
  - 8 to <10 hours after
Statistical analysis
- Multivariable logistic regression
- Adjustments
  - Maternal age | BMI | Race/ethnicity | Modified Bishop score on admission | Treatment group | Hospital
Primary outcome
- Cesarean delivery
Secondary outcomes
- Maternal and neonatal complications

2,854 (46.7% of women from the parent trial) met inclusion criteria
- Amniotomy: 82.0%
  - The majority were performed between 2 and <6 hours after oxytocin
After adjusting for confounders, only 6 to <8 hours after oxytocin was associated with lower cesarean rates
- Amniotomy 6 to <8 hours after oxytocin: 21.9% cesarean rate
- Without amniotomy: 29.7% cesarean rate
- Adjusted odds ratio (OR) 0.61 (95% CI, 0.42 to 0.89)
Amniotomy at time intervals ≥4 hours after oxytocin was associated with lower odds of labor lasting more than 24 hours
- 4 to <6 hours after oxytocin: aOR 0.59 (99% CI, 0.41–0.86)
- 6 to <8 hours after oxytocin: aOR 0.38 (99% CI, 0.24–0.61)
- 8 to <10 hours after oxytocin: aOR 0.37 (99% CI, 0.21–0.64)
Amniotomy at time intervals ≥2 hours and <8 hours after oxytocin was associated with lower odds of maternal hospitalization >3 days
There was no association between amniotomy and postpartum or neonatal complications including
- Chorioamnionitis | PPH | Infection | NICU admission

For nulliparous women at term, amniotomy during induction was associated with a risk of cesarean similar or lower compared to that of women with no amniotomy and may be associated with a shorter labor duration

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