Association of placental weight with cerebral palsy: population-based cohort study in Norway

Abstract

Objective: To study the risk of cerebral palsy (CP) associated with placental weight, and also with placental weight/birthweight ratio and placental weight/birth length ratio.

Design: Population-based cohort study.

Setting: Perinatal data in the Medical Birth Registry of Norway were linked with clinical data in the CP Register of Norway.

Population: A total of 533 743 singleton liveborn children in Norway during 1999-2008. Of these, 779 children were diagnosed with CP.

Methods: Placental weight, placental weight/birthweight ratio, and placental weight/birth length ratio were grouped into gestational age-specific quartiles. Odds ratios (OR) with 95% confidence intervals (95% CI) for CP were calculated for children with exposure variables in the lowest or in the highest quartile, using the second to third quartile as the reference.

Main outcome measures: CP and CP subtypes.

Results: Overall, children with low placental weight had increased risk for CP (OR 1.5, 95% CI 1.2-1.7). Low placental weight/birthweight ratio (OR 1.2, 95% CI 1.0-1.4) and low placental weight/birth length ratio (OR 1.5, 95% CI 1.2-1.8) were also associated with increased risk for CP. In children born at term, low placental weight was associated with a twofold increase in risk for spastic bilateral CP (including both quadriplegia and diplegia) (OR 2.1, 95% CI 1.5-2.9). In children born preterm, high placental ratios were associated with increased risk for spastic quadriplegia.

Conclusions: Our results suggest that placental dysfunction may be involved in causal pathways leading to the more severe subtypes of CP.

Tweetable abstract: Low placental weight increases the risk for cerebral palsy, especially for the spastic bilateral subtype.

Keywords: Birthweight; epidemiology; placenta; pregnancy; risk factors.