Grand Rounds

Are Adverse Outcomes More Frequent with Delivery at 40 or 41 Weeks vs 39 Weeks?

BACKGROUND AND PURPOSE:

Chen et al. (Obstetrics and Gynecology 2019) compared maternal and neonatal morbidity among low-risk, nulliparous full-term women delivered at 39 weeks vs 40 and 41 weeks

Population-based cohort study
- Low-risk
- Nulliparous women
- Main exposure: Gestational week at delivery
  - 39, 40, or 41 weeks
Primary outcome: Composite neonatal morbidity included any of following
- Apgar score <5 at 5 minutes
- Assisted ventilation >6 hours
- Seizure
- Mortality (death within 27 days)
Secondary outcome: Composite maternal morbidity, included any of the following
- ICU admission
- Blood transfusion
- Uterine rupture
- Unplanned hysterectomy
Statistical analysis
- Multivariate Poisson regression to estimate association between gestational age and morbidity
- Primary and secondary outcomes were adjusted for confounders
- 39 week used as reference

3.3 million live births included in analysis
- 43.5% at 39 weeks | 41.4% at 40 weeks | 15.1% at 41 weeks
Overall composite neonatal morbidity: 8.8/1000 live births
Overall composite maternal morbidity: 2.8/1000 live births

Newborn morbidity

When compared to 39 weeks of gestation, neonatal morbidity was higher at
- 40 weeks: Adjusted relative risk (RR) 1.22 (95% CI, 1.19–1.25)
- 41 weeks: aRR 1.53 (95% CI, 1.49–1.58)

Maternal morbidity

When compared to 39 weeks of gestation, maternal morbidity was higher at
- 40 weeks: aRR 1.19 (95% CI, 1.14–1.25)
- 41 weeks: aRR 1.56 (95% CI, 1.47–1.65)

Both neonatal and maternal morbidity were higher in 40 and 41 week cohort compared to 39 week reference
While composite morbidity rates were overall low, the implications for pregnant women are significant
The authors suggest that the findings from this study can be used in shared decision making regarding induction at 39 weeks for women who are nulliparous and at otherwise low risk

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