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Table 1 Characteristics of mother-infant pairs included and excluded in the study

From: Prenatal exposure to perfluoroalkyl substances and thyroid hormone concentrations in cord plasma in a Chinese birth cohort

Variablesa Participants included
(N = 300)
n (%)
Participants excluded
(N = 925)
n (%)
P-value of Student’s t-test or Chi-square test
Maternal age at birth (years, mean ± SD) 27.5 ± 3.5 27.9 ± 3.4 0.0592
Maternal pre-pregnant BMI (kg/m2)
 < 18.5 63 (21.4) 181 (19.9) 0.8633
 18.5–24.9 218 (73.9) 683 (75.1)  
 ≥ 25.0 14 (4.7) 45 (5.0)  
Parity
 Nulliparous 261 (87.0) 767 (83.7) 0.1744
 Multiparous 39 (13.0) 149 (16.3)  
Maternal education
 High school or less 68 (22.7) 226 (24.5) 0.5460
 College or higher 231 (77.3) 698 (75.5)  
Per capita household income (CNY/month)
 < 4000 66 (22.1) 187 (20.5) 0.2290
 4000–8000 130 (43.5) 359 (39.5)  
 > 8000 103 (34.4) 364 (40.0)  
Maternal passive smoking before conception
 No 171 (57.2) 556 (60.3) 0.3406
 Yes 128 (42.8) 366 (39.7)  
Gestational age (weeks)
 ≥ 37 295 (98.3) 884 (95.7) 0.0332
 < 37 5 (1.7) 40 (4.3)  
Type of delivery
 Vaginal 154 (51.7) 368 (46.5) 0.1246
 Cesarean section 144 (48.3) 424 (53.5)  
Child’s sex
 Male 167 (55.6) 500 (54.2) 0.6642
 Female 133 (44.4) 422 (45.8)  
  1. aSD Standard deviation, BMI Body mass index, CNY Chinese Yuan
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