BACKGROUND AND PURPOSE:

• Interactions between risk factors for stillbirth are not well characterized
• Lindegren et al. (BJOG, 2021) investigated interactions between gestational age (≥39 weeks), BMI and parity on stillbirth or neonatal death

METHODS:

• Retrospective study
• Population
  • Singleton, cephalic births at gestational duration
  • 39w0d to 42w2d
• Exposure
  • Parity
  • Maternal BMI
• Study design
  • Relative risk ratios (RR) for mortality in relation to gestational duration were stratified by exposure
  • Relative RRs were adjusted for maternal age, smoking, country of birth, and educational level
• Primary outcome
  • Stillbirth or neonatal death <45 post-menstrual weeks
• Secondary outcome
  • Stillbirth

RESULTS:

• 892,339 births
• Among primiparous women, infants born at ≥41w3d were at increased risk of stillbirth or neonatal death before <45 post-menstrual weeks vs 39w0d to 40w2d
  • aRR 1.29 (95% CI, 1.10 to 1.52)
• Primiparous women: Gestational age risk was modulated by BMI
  • BMI <25: aRR 1.04 (95% CI, 0.81 to 1.34)
  • BMI 25 to 29.9: aRR 1.25 (95% CI, 0.94 to 1.66)
  • BMI ≥30: aRR 1.52 (95% CI, 1.10 to 2.10)
• Among primiparous women, the risk of stillbirth increased with gestational duration in all BMI strata, with the highest risk increase for BMI ≥30
  • At 40w3d to 40w6d: 0.8 of every 1000 births
  • At 42w0d to 42w2d: 4.0 of every 1000 births
• Multiparous women: No significant increase in risk with increased gestational age, regardless of BMI

CONCLUSION:

• Among primiparous women, pregnancies lasting more than 41w3d were at increased risk for stillbirth or neonatal death <45 weeks post-menstruation
  • This risk was higher in women with BMI ≥30
• For multiparous women, there was no significant association with gestational duration and neonatal mortality
• The authors state

The risk for stillbirth (our secondary outcome) in pregnancies at 39+0 weeks of gestation and beyond was more than doubled among primiparous compared with multiparous women

To our knowledge, no other study has been published that report fetal and neonatal deaths by BMI discretely for primiparous and multiparous women

Learn More – Primary Sources:

Stillbirth or neonatal death before 45 post-menstrual weeks in relation to gestational duration in pregnancies at 39 weeks or beyond: the impact of parity and body mass index. A national cohort study

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