Placental weight for gestational age and adverse perinatal outcomes

Obstetrics and Gynecology, 06/04/2012

Placental weight for gestational age is an independent risk factor for adverse perinatal outcomes, above and beyond the known association with birth weight. The mechanisms behind the opposing effects of placental weight z score on risk of stillbirth compared with adverse neonatal outcomes require further elucidation.


  • A sex– and gestational age–specific placental weight z score was calculated for a cohort of 87,600 singleton births at the Royal Victoria Hospital in Montreal, Canada, 1978–2007.
  • The relationship between placental weight z score and adverse perinatal outcomes (stillbirth, neonatal death, 5–minute Apgar score lower than 7, seizures, or respiratory morbidity) was examined using logistic regression.
  • Multivariable models examined whether the relationship was independent of birth weight and other pregnancy risk factors.


  • After controlling for birth weight, fetuses with a low placental weight z score were at significantly increased risk of stillbirth (odds ratio [OR] 2.0, 95% confidence interval [CI] 1.4–2.6, percent population attributable risk 17.8%).
  • In contrast, adverse neonatal outcomes were significantly more likely among those with high placental weight z scores (OR 1.4, 95% CI 1.2–1.7, percent population attributable risk 5% for any serious neonatal morbidity).
  • Similar trends were observed after further adjusting for pregnancy risk factors.

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