BACKGROUND AND PURPOSE:

• Tingleff et al. (BJOG, 2021) assessed risk for recurrent preterm birth with a focus on the presence of placental disorders

METHODS:

• Population-based registry study
  • Norwegian registry
• Population
  • First and second singleton child born between 1999 and 2014
• Exposures
  • Preterm first birth
  • Term first birth used as reference
• Study design
  • Preterm birth definitions
    • Extremely preterm: <28w0d
    • Very preterm: 28w0d to 33w6d  
    • Late preterm: 34w0d to 36w6d
  • Placental disorders
    • Preeclampsia | HELLP | Eclampsia | SGA (birthweight <5%tile)
  • Multivariate logistic regression analyses were performed
  • Adjustments: Placental disorders | Maternal and obstetric history | Socioeconomic factors | Known risk factors for preterm birth
• Primary outcome
  • Preterm second birth

RESULTS:

• 213,335 women | 426,670 births
• Preterm birth (<37 weeks) rates
  • First births: 5.6%
  • Second births: 3.7%
• Among women with any category of preterm first birth, 17.4% had a preterm second birth
• Extremely preterm second births occurred most frequently among women with an extremely preterm first birth
  • Extremely preterm second birth incidence: 0.2%
  • Adjusted odds ratio (aOR) 12.90 (95% CI, 7.47 to 22.29)
• Very preterm second births occurred most frequently after an extremely preterm birth
  • Very preterm second birth incidence: 0.7%
  • aOR 12.98 (95% CI, 9.59 to 17.58)
• Late preterm second births occurred most frequently after a previous very preterm birth
  • Late preterm second birth incidence: 2.8%
  • aOR 6.86 (95% CI, 6.11 to 7.70)
• The contribution of placental disorders was most pronounced for recurrent extremely and very preterm birth
  • Placental disorder in both births vs no placental disorder
    • 5.7-fold increase in odds of having an extremely preterm second birth (aOR, 5.72; CI, 4.03-8.12)
    • 6.6-fold increase in the odds of having a very preterm second birth (aOR, 6.63; CI, 5.67–7.75)
    • 3.6-fold increase in odds of late preterm second birth (aOR, 3.58; CI, 3.22–3.98)

CONCLUSION:

• Approximately 1 in 6 women will experience a preterm second birth
• Placental disorder contribution was more pronounced for recurrent extremely and very preterm birth than for recurrent late preterm birth
• The authors state

Placental disorders explained 30~40% of the increased odds for having an extremely or very preterm second birth and explained 10~22% of the increased odds for having a late preterm second birth

Learn More – Primary Sources:

Risk of preterm birth in relation to history of preterm birth: a population-based registry study of 213,335 women in Norway

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