Evidence Matters

Does a Prior C-Section Increase Risk of Preterm Birth in Later Pregnancies?

BACKGROUND AND PURPOSE:

Vahanian et al. (AJOG, 2019) evaluated whether there is an association between term cesarean delivery in the first pregnancy and subsequent spontaneous or indicated preterm delivery in women with uncomplicated pregnancies

Retrospective cohort study
Participants
- Two consecutive singleton deliveries
- Excluded women with known medical or obstetrical complications during the first pregnancy
Groups
- Preceded by cesarean group: First pregnancy resulting with cesarean delivery at term
- Preceded by vaginal delivery group: First pregnancy resulting with vaginal delivery at term
Data collection and analysis
- Identification via linked pregnancy database at a single institution
- Logistic regression to determine associations
Primary outcome
- Overall preterm delivery <37 weeks in the second pregnancy
Secondary outcomes
- Type of preterm delivery: Spontaneous vs Indicated
- Timing of preterm delivery: Late preterm delivery (34w0d to 36w6d) or early preterm delivery (<34 weeks)
- SGA (birthweight <5th percentile)

6456 linked pregnancies | 2284 were matched
- Preceded by cesarean group: 1142
- Preceded by vaginal delivery group: 1142
The main indications for cesarean in the first pregnancy were
- Dystocia: 61.5%
- Nonreassuring fetal status: 19.4%
- Breech: 8.8%
- Other: 7.4%
The mean (SD) gestational ages at delivery for the second pregnancy was
- Preceded by cesarean group: 38.8 (1.8) weeks
- Preceded by vaginal delivery group: 38.9 (1.7) weeks
The risks of preterm delivery in the second pregnancy
- Preceded by cesarean group: 6.0%
- Preceded by vaginal delivery group: 5.2%
- adjusted odds ratio (OR) 1.46 (95% CI, 0.77 to 2.76)
No associations were seen between cesarean delivery in the first pregnancy and
- Spontaneous preterm delivery
  - Preceded by cesarean group: 4.6%
  - Preceded by vaginal delivery group: 3.9%
  - aOR 1.40 (95% CI, 0.59 to 3.32)
- Indicated preterm delivery
  - Preceded by cesarean group: 1.6%
  - Preceded by vaginal delivery group: 1.4%
  - aOR 1.21 (95% CI, 0.60 to 2.46)
No significant differences were found in
- Late preterm delivery
  - Preceded by cesarean group: 4.6%
  - Preceded by vaginal delivery group: 4.1%
  - aOR 1.13 (95% CI, 0.55 to 2.29)
- Early preterm delivery
  - Preceded by cesarean group: 1.6%
  - Preceded by vaginal delivery group: 1.2%
  - aOR 1.25 (95% CI, 0.59 to 2.67)
- Neonates with
  - Preceded by cesarean group: 3.6%
  - Preceded by vaginal delivery group: 2.2%
  - aOR 1.26 (95% CI, 0.52 to 3.06)

In women with no other medical or obstetric complications, prior cesarean delivery is not associated with an increased risk of spontaneous or indicated preterm delivery

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