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Table 1 Comparison of maternal/child characteristics between children completing the neurodevelopmental assessment and those who did not

From: Maternal methylmercury exposure through rice ingestion and child neurodevelopment in the first three years: a prospective cohort study in rural China

  

Follow-up at 12 months

Follow-up at 36 months

All (n = 391)

n (%)

No (N = 127, 32%)

n (%)

Yes (N = 264, 68%)

n (%)

p-value

No (N = 201, 51%)

n (%)

Yes (N = 190, 49%)

n (%)

p-value

Mother’s Age upon Enrollment (years)

 Age < 20

28 (7)

8 (6.3)

20 (7.6)

0.48

14 (7)

14 (7.4)

0.96

 20 ≤ Age < 30

223 (57)

68 (54)

155 (59)

 

116 (58)

107 (56)

 

 30 ≤ Age < 45

140 (36)

51 (40)

89 (34)

 

71 (35)

69 (36)

 

Mother’s Ethnicity

 Zhuang

333 (85)

104 (82)

229 (87)

0.28

168 (84)

165 (87)

0.58

 Han

50 (13)

21 (17)

29 (11)

 

29 (14)

21 (11)

 

 Other

8 (2)

2 (1.6)

6 (2.3)

 

4 (2.0)

4 (2.1)

 

Mother’s Education Completed

  < High School

316 (81)

110 (87)

206 (78)

0.04*

170 (85)

146 (77)

0.07

 High School

47 (12)

9 (7.1)

38 (14)

 

19 (9.5)

28 (15)

 

 Some University

18 (4.6)

3 (2.4)

15 (5.7)

 

6 (3.0)

12 (6.3)

 

 Missing

10 (2.6)

5 (3.9)

5 (1.9)

 

6 (3.0)

4 (2.1)

 

Father’s Education Completed

  < High School

304 (78)

103 (81)

201 (76)

0.22

164 (82)

140 (74)

0.02*

 High School

57 (15)

14 (11)

43 (16)

 

25 (12)

32 (17)

 

 Some University

20 (5.1)

4 (3.1)

16 (6.7)

 

5 (2.5)

15 (7.9)

 

 Missing

10 (2.6)

6 (4.7)

4 (1.5)

 

7 (3.5)

3 (1.6)

 

Mother’s Occupation

 Farmer

298 (76)

108 (85)

190 (72)

0.015*

158 (79)

140 (74)

0.50

 Workera

31 (7.9)

6 (4.7)

25 (9.5)

 

12 (6.0)

19 (10)

 

 Unemployed

42 (11)

9 (7.1)

33 (13)

 

21 (10)

21 (11)

 

 Other

13 (3.3)

1 (< 1)

12 (4.5)

 

7 (3.5)

6 (3.2)

 

 Missing

7 (1.8)

3 (2.4)

4 (1.5)

 

3 (1.5)

4 (2.1)

 

Father’s Occupation

 Farmer

289 (74)

101 (80)

188 (71)

0.08

155 (77)

134 (71)

0.046*

 Workera

53 (14)

13 (10)

40 (15)

 

18 (9.0)

35 (18)

 

 Unemployed

23 (5.9)

5 (3.9)

18 (6.8)

 

14 (7.0)

9 (4.7)

 

 Other

17 (4.3)

2 (1.2)

15 (5.7)

 

8 (4.0)

9 (4.7)

 

 Missing

9 (2.3)

6 (4.7)

3 (1.1)

 

6 (3.0)

3 (1.6)

 

Household Monthly Income (RMB)b

 Income < 2000

230 (59)

68 (54)

162 (61)

0.26

114 (57)

116 (61)

0.72

 2000 ≤ Income < 5000

107 (27)

39 (31)

68 (26)

 

58 (29)

49 (26)

 

 Income ≥5000

19 (4.9)

8 (6.3)

11 (4.2)

 

10 (5.0)

9 (4.7)

 

 Missing

35 (9.0)

12 (9.4)

23 (8.7)

 

19 (9.5)

16 (8.4)

 

Maternal Pre-Pregnancy BMI (kg/m2)c

 Underweight

90 (23)

21 (17)

69 (26)

0.07

39 (19)

51 (27)

0.33

 Normal Weight

231 (59)

82 (65)

149 (56)

 

126 (63)

105 (55)

 

 Overweight

60 (15)

23 (18)

37 (14)

 

30 (15)

30 (16)

 

 Obese

9 (2.3)

1 (< 1)

8 (3.3)

 

5 (2.5)

4 (2.1)

 

 Missing

1 (< 1)

0 (0)

1 (< 1)

 

1 (< 1)

0 (0)

 

Maternal Smoking During Pregnancy

 No

377 (96)

117 (92)

260 (98)

0.003**

191 (95)

186 (98)

0.37

 Yes

5 (1.3)

5 (3.9)

0 (0)

 

4 (2.0)

1 (< 1)

 

 Missing

9 (2.3)

5 (3.9)

4 (1.6)

 

6 (3.0)

3 (1.6)

 

2nd-Hand Smoke Exposure During Pregnancy

 No

214 (55)

65 (51)

149 (56)

0.41

100 (50)

114 (60)

0.06

 Yes

163 (42)

56 (44)

107 (41)

 

92 (46)

71 (37)

 

 Missing

14 (3.6)

6 (4.7)

8 (3.3)

 

9 (4.5)

5 (2.6)

 

Alcohol During Pregnancy

 No

379 (97)

121 (95)

258 (98)

1.0

196 (98)

183 (96)

0.36

 Yes

4 (1.0)

1 (< 1)

3 (1.1)

 

1 (< 1)

3 (1.6)

 

 Missing

8 (2.0)

5 (3.9)

3 (1.1)

 

4 (2.0)

4 (2.1)

 

Anemia During Pregnancy

 No

377 (96)

123 (97)

254 (96)

0.56

193 (96)

184 (97)

1.0

 Yes

13 (3.3)

3 (2.4)

10 (3.8)

 

7 (3.5)

6 (3.2)

 

 Missing

1 (< 1)

1 (< 1)

0 (0)

 

1 (< 1)

0 (0)

 

Primipara

 No

185 (47)

66 (52)

119 (45)

0.20

97 (48)

88 (46)

0.64

 Yes

190 (49)

56 (44)

134 (51)

 

95 (47)

95 (50)

 

 Missing

16 (4.1)

5 (3.9)

11 (4.2)

 

9 (4.5)

7 (3.7)

 

Maternal Rice Consumption

  < Daily

47 (12)

12 (9.4)

35 (13)

0.26

23 (11)

24 (13)

0.72

  ≥ Daily

323 (83)

109 (86)

214 (81)

 

167 (83)

156 (82)

 

 Missing

21 (5.4)

6 (4.7)

15 (5.7)

 

11 (5.5)

10 (5.3)

 

Maternal Fish Consumption (servings/week)

 0 servings/week

169 (43)

60 (47)

109 (41)

0.33

87 (43)

82 (43)

0.87

 0 < servings/week < 2

178 (46)

51 (40)

127 (48)

 

93 (46)

85 (45)

 

  ≥ 2 servings/week

44 (11)

16 (13)

28 (11)

 

21 (10)

23 (12)

 

Cesarean Birth

 No

285 (73)

91 (72)

194 (27)

0.70

138 (69)

147 (77)

0.05*

 Yes

106 (27)

36 (28)

70 (73)

 

63 (31)

43 (23)

 

Child Sex

 Male

198 (51)

53 (42)

140 (53)

0.04*

94 (47)

104 (55)

0.12

 Female

193 (49)

74 (58)

124 (47)

 

107 (53)

86 (45)

 

Gestational Age (weeks)

 37 ≤ Gestational Age < 39

151 (39)

55 (43)

96 (36)

0.22

81 (40)

70 (37)

0.54

 39 ≤ Gestational Age < 41

215 (55)

68 (54)

147 (56)

 

110 (55)

105 (55)

 

 Gestational Age ≥ 41

22 (5.6)

4 (3.2)

18 (6.8)

 

9 (4.5)

13 (6.8)

 

 Missing

3 (< 1)

0 (0)

3 (1.1)

 

1 (< 1)

2 (1.1)

 

Birth weight-for-gestational age z-score (centile)d

 Value < 10th

45 (12)

13 (10)

32 (12)

0.41

20 (10)

25 (13)

0.47

 10th ≤ Value <90th

327 (84)

111 (87)

216 (81)

 

173 (86)

154 (81)

 

 Value ≥90th

16 (4.1)

3 (2.4)

13 (4.9)

 

7 (3.5)

9 (4.7)

 

 Missing

3 (< 1)

0 (0)

3 (1.1)

 

1 (< 1)

2 (1.1)

 

Questionnaire Responses at 12 or 36 Months

 Primary Caregiver

  Mother

NA

NA

208 (79)

NA

NA

115 (61)

NA

  Father

NA

NA

32 (12)

 

NA

23 (12)

 

  Grandparent

NA

NA

24 (9.1)

 

NA

52 (27)

 

  Other relative

NA

NA

0 (0)

 

NA

0 (0)

 

 Mother or Father is a Migrant Worker

  No

NA

NA

251 (95)

NA

NA

149 (78)

NA

  Yes

NA

NA

9 (3.5)

 

NA

41 (22)

 

  Missing

NA

NA

4 (1.5)

  

0 (0)

 

 Older Child in the Household

  No

NA

NA

160 (61)

NA

NA

102 (54)

NA

  Yes

NA

NA

104 (39)

 

NA

86 (45)

 

  Missing

NA

NA

0 (0)

 

NA

2 (1.1)

 

 Breastfeeding Duration > Median (8.5 months)e

  No

NA

NA

127 (48)

NA

NA

89 (47)

NA

  Yes

NA

NA

136 (52)

 

NA

100 (53)

 

  Missing

NA

NA

1 (< 1)

 

NA

1 (< 1)

 
  1. *p ≤ 0.05, **p < 0.01, p-values are for chi-squared test or Fisher’s exact test between non-missing categories
  2. BMI body mass intake, RMB ren min bi = Chinese currency
  3. aWorkers include: civil servant, white-collar worker, skilled worker, unskilled worker, and shopkeeper
  4. bBetween 2013–2014, 2000 RMB = US$324, US$5000 RMB = $810
  5. cBMI for Asian populations: underweight (BMI < 18.5 kg/m2), normal weight (18.5 kg/m2 ≤ BMI < 23 kg/m2), overweight (23 kg/m2 ≤ BMI < 27.5 kg/m2), and obese (BMI ≥ 27.5 kg/m2) [12]
  6. dBirth weight-for-gestational age z-scores were calculated using the Intergrowth-21 Newborn Birth standards, which were based on a reference population of 20,486 births from eight countries including 17% from China [13]
  7. eMedian breastfeeding duration based on 12-month and 36-month responses (n = 332 mothers)