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Table 1 The characteristics of the study population (n = 1442)

From: In utero exposure to mercury and childhood overweight or obesity: counteracting effect of maternal folate status

 Maternal RBC mercury level (μg/L) in quartiles
Q1
0·39–1·04
Q2
1·02–2·10
Q3
2·12–3·68
Q4
3·70–27·8
P trend
Maternal characteristics
n360361359362 
Age, years26·8 ± 6·528·0 ± 6·029·1 ± 6·730·3 ± 6·3< 0·001
Race    < 0·001
 Black192 (53·3)225 (62·3)265 (73·8)285 (78·7) 
 Non-black168 (46·7)136 (37·7)94 (26·2)77 (21·3) 
Education    0·367
 High school and less234 (65·0)243 (67·3)233 (64·9)226 (62·4) 
 Beyond high school126 (35·0)118 (32·7)126 (35·1)136 (37·6) 
Smoking    < 0·001
 Not smoker279 (77·5)284 (78·7)305 (85·0)324 (89·5) 
 Smoker81 (22·5)77 (21·3)54 (15·0)38 (10·5) 
Parity    0·001
 Nulliparous177 (49·2)150 (41·6)139 (38·7)136 (37·6) 
 Multiparous183 (50·8)211 (58·4)220 (61·3)226 (62·4) 
 Pre-pregnancy BMI, kg/m226·4 ± 6·827·2 ± 7·627·2 ± 6·726·5 ± 5·70·769
 Overweight or obesity176 (48·9)185 (51·2)203 (56·6)197 (54·4)0·063
 Diabetes44 (12·2)45 (12·5)45 (12·5)50 (13·8)0·537
 Hypertensive disorder45 (12·5)50 (13·9)61 (17·0)60 (16·6)0·068
Fish intake (serving/week)    < 0·001
 0163 (45·3)80 (22·2)55 (15·3)35 (9·7) 
 1–2183 (50·8)253 (70·1)246 (68·5)239 (66·0) 
 ≥ 314 (3·9)28 (7·7)58 (16·2)88 (24·3) 
 Plasma folate (nmol/L)*34·6 (32·5–36·8)30·1 (28·3–32·1)29·4 (27·5–31·3)30·7 (28·8–32·7)< 0·001
Child’s characteristics
Age, years7·6 ± 2·98·0 ± 3·28·6 ± 3·38·4 ± 3·00·001
Gender    0·002
 Boy196 (54·4)190 (52·6)180 (50·1)156 (43·1) 
 Girl164 (45·6)171 (47·4)179 (49·9)206 (56·9) 
Birthweight, g2982 ± 7732955 ± 7762972 ± 7903015 ± 8180·775
Gestational age, weeks38·0 ± 3·237·9 ± 3·337·8 ± 3·238·1 ± 3·10·998
Preterm birth88 (24·4)90 (24·9)85 (23·7)85 (23·5)0·681
Fetal growth    0·176
 AGA290 (80·6)286 (79·2)279 (77·7)281 (77·6) 
 SGA38 (10·5)37 (10·3)39 (10·9)37 (10·2) 
 LGA32 (8·9)38 (10·5)41 (11·4)44 (12·2) 
Breastfeeding    0·013
 Formula only90 (25·0)105 (29·1)88 (24·5)65 (17·9) 
 Breastfeed exclusively28 (7·8)31 (8·6)21 (5·9)39 (10·8) 
 Both242 (67·2)225 (62·3)250 (69·6)258 (71·3) 
Overweight or obesity138 (38·3)154 (42·7)146 (40·7)174 (48·1)0·019
Number of BMI measures3·8 ± 2·34·0 ± 2·54·1 ± 2·64·0 ± 2·4< 0·001
  1. *Geometric mean (95% CI); Q quartile, RBC red blood cell, AGA appropriate for gestational age, SGA small for gestational age, LGA large for gestational age