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Table 1 Study population characteristics

From: Placental mitochondrial DNA content is associated with childhood intelligence

Parental characteristics (n = 201)
Education
 Low 16 (8.0)
 Middle 71 (35.3)
 High 114 (56.7)
Neighbourhood income, euro 18,483 ± 2474
Smoking during pregnancy 16 (8.0)
Cigarettes/day during pregnancy 1.5 ± 3.7
Urban environment within 5 km, % 32 ± 12
Characteristics of twins (n = 375)
Birth  
Birth weight (g) 2525 ± 514
Gestational age, weeks 36.8 ± 2.3
Birth year 1986 ± 2.5
Sex  
 Male–male 143 (38.1)
 Female–female 131 (34.9)
 Male–female 101 (26.9)
Zygosity–chorionicity  
 Dizygotic-dichorionic 212 (56.5)
 Monozygotic-dichorionic 73 (19.5)
 Monozygotic-monochorionic 90 (24.0)
Twins in final study  
 Twin with 1 individual in study 27 (7.0)
 Twin with 2 individuals in study 348 (93.0)
Childhood  
Age 11.5 ± 1.6
Intelligence score (IQ)  
 Total IQ 106.0 ± 15.1
 Verbal 106.6 ± 14.6
 Performance 103.9 ± 15.3
  1. Data presented are mean ± standard deviation or number (percentage)