Table 1 The characteristics of the study population (n = 1442)
|  | 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 | |||||
n | 360 | 361 | 359 | 362 | Â |
Age, years | 26·8 ± 6·5 | 28·0 ± 6·0 | 29·1 ± 6·7 | 30·3 ± 6·3 | < 0·001 |
Race |  |  |  |  | < 0·001 |
 Black | 192 (53·3) | 225 (62·3) | 265 (73·8) | 285 (78·7) |  |
 Non-black | 168 (46·7) | 136 (37·7) | 94 (26·2) | 77 (21·3) |  |
Education |  |  |  |  | 0·367 |
 High school and less | 234 (65·0) | 243 (67·3) | 233 (64·9) | 226 (62·4) |  |
 Beyond high school | 126 (35·0) | 118 (32·7) | 126 (35·1) | 136 (37·6) |  |
Smoking |  |  |  |  | < 0·001 |
 Not smoker | 279 (77·5) | 284 (78·7) | 305 (85·0) | 324 (89·5) |  |
 Smoker | 81 (22·5) | 77 (21·3) | 54 (15·0) | 38 (10·5) |  |
Parity |  |  |  |  | 0·001 |
 Nulliparous | 177 (49·2) | 150 (41·6) | 139 (38·7) | 136 (37·6) |  |
 Multiparous | 183 (50·8) | 211 (58·4) | 220 (61·3) | 226 (62·4) |  |
 Pre-pregnancy BMI, kg/m2 | 26·4 ± 6·8 | 27·2 ± 7·6 | 27·2 ± 6·7 | 26·5 ± 5·7 | 0·769 |
 Overweight or obesity | 176 (48·9) | 185 (51·2) | 203 (56·6) | 197 (54·4) | 0·063 |
 Diabetes | 44 (12·2) | 45 (12·5) | 45 (12·5) | 50 (13·8) | 0·537 |
 Hypertensive disorder | 45 (12·5) | 50 (13·9) | 61 (17·0) | 60 (16·6) | 0·068 |
Fish intake (serving/week) |  |  |  |  | < 0·001 |
 0 | 163 (45·3) | 80 (22·2) | 55 (15·3) | 35 (9·7) |  |
 1–2 | 183 (50·8) | 253 (70·1) | 246 (68·5) | 239 (66·0) |  |
 ≥ 3 | 14 (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, years | 7·6 ± 2·9 | 8·0 ± 3·2 | 8·6 ± 3·3 | 8·4 ± 3·0 | 0·001 |
Gender |  |  |  |  | 0·002 |
 Boy | 196 (54·4) | 190 (52·6) | 180 (50·1) | 156 (43·1) |  |
 Girl | 164 (45·6) | 171 (47·4) | 179 (49·9) | 206 (56·9) |  |
Birthweight, g | 2982 ± 773 | 2955 ± 776 | 2972 ± 790 | 3015 ± 818 | 0·775 |
Gestational age, weeks | 38·0 ± 3·2 | 37·9 ± 3·3 | 37·8 ± 3·2 | 38·1 ± 3·1 | 0·998 |
Preterm birth | 88 (24·4) | 90 (24·9) | 85 (23·7) | 85 (23·5) | 0·681 |
Fetal growth |  |  |  |  | 0·176 |
 AGA | 290 (80·6) | 286 (79·2) | 279 (77·7) | 281 (77·6) |  |
 SGA | 38 (10·5) | 37 (10·3) | 39 (10·9) | 37 (10·2) |  |
 LGA | 32 (8·9) | 38 (10·5) | 41 (11·4) | 44 (12·2) |  |
Breastfeeding |  |  |  |  | 0·013 |
 Formula only | 90 (25·0) | 105 (29·1) | 88 (24·5) | 65 (17·9) |  |
 Breastfeed exclusively | 28 (7·8) | 31 (8·6) | 21 (5·9) | 39 (10·8) |  |
 Both | 242 (67·2) | 225 (62·3) | 250 (69·6) | 258 (71·3) |  |
Overweight or obesity | 138 (38·3) | 154 (42·7) | 146 (40·7) | 174 (48·1) | 0·019 |
Number of BMI measures | 3·8 ± 2·3 | 4·0 ± 2·5 | 4·1 ± 2·6 | 4·0 ± 2·4 | < 0·001 |