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Table 1 Baseline characteristics of two sub-study subjects

From: The effect of pre-pregnancy hair dye exposure on infant birth weight: a nested case-control study

Characteristics

LBW group (n = 315)

Macrosomia group (n = 381)

LBW (%)

NBW (%)

P a

Macrosomia (%)

NBW (%)

P a

N

105

210

 

127

254

 

Maternal age (years) [mean (SD)]

28 (4.7)

28.2 (4.9)

0.753

29.9 (5.2)

27.7 (4.8)

<  0.001

Pre-pregnant height (cm) [mean (SD)]

156.1 (4.3)

157.7 (4.7)

0.003

56.8 (8.6)

50 (7.6)

<  0.001

Pre-pregnant weight (kg) [mean (SD)]

47.8 (7.5)

51 (8.3)

0.001

158.4 (4.6)

157.3 (4.8)

0.047

Pre-pregnant BMI categories (kg /m 2)

  

0.073

  

<  0.001

  < 18.5

40 (38.5)

56 (26.7)

 

8 (6.5)

78 (30.7)

 

 18.5–23.9

55 (52.9)

125 (59.5)

 

79 (63.7)

153 (60.2)

 

  ≥ 24

9 (8.7)

29 (13.8)

 

37 (29.8)

23 (9.1)

 

Age at menarche (years) [mean (SD)]

13.4 (1.5)

13.5 (1.5)

0.846

13.3 (2.1)

13.6 (1.7)

0.184

Gravidity history

  

0.212

  

0.073

 First

44 (41.9)

67 (31.9)

 

28 (22.0)

71 (28.0)

 

 2–3

46 (43.8)

106 (50.5)

 

69 (54.3)

146 (57.5)

 

  > 3

15 (14.3)

37 (17.6)

 

30 (23.6)

37 (14.6)

 

Parity history

  

0.145

  

0.017

 First

37 (35.2)

92 (43.8)

 

71 (55.9)

109 (42.9)

 

  ≥ 2

68 (64.8)

118 (56.2)

 

56 (44.1)

145 (57.1)

 

Menstrual regularity

  

<  0.001

  

0.009

 Yes

74 (70.5)

183 (87.1)

 

92 (72.4)

212 (83.8)

 

Education level (years)

  

0.909

  

<  0.001

  ≤ 9

38 (36.2)

72 (34.3)

 

68 (53.5)

85 (33.5)

 

 10–12

32 (30.5)

63 (30.0)

 

30 (23.6)

72 (28.4)

 

  ≥ 13

35 (33.3)

75 (35.7)

 

29 (22.8)

97 (39.2)

 

Alcohol use pre-pregnancy

  

0.854

  

0.094

 Yes

27 (25.7)

52 (24.8)

 

70 (27.6)

25 (19.7)

 

Smoking status

  

0.213

  

0.554

 Current / ex-smoker

3 (2.9)

1 (0.5)

 

2 (0.8)

0 (0)

 

Second-hand smoking

  

0.657

  

0.257

 Yes

16 (15.2)

28 (13.4)

 

26 (10.2)

18 (14.2)

 

Progesterone use pre-pregnancy

  

0.282

  

0.857

 Yes

1 (1.0)

8 (3.8)

 

11 (4.3)

5 (3.9)

 

Progesterone use during pregnancy

  

0.375

  

1.000

 Yes

26 (24.8)

62 (29.5)

 

38 (29.9)

76 (29.9)

 
  1. Abbreviations: LBW low birth weight, NBW new birth weight, SD standard deviation, % percentages estimated on valid data only, BMI body mass index is measured and defined as weight (kg) / height (m) 2
  2. aT-tests and Chi-square tests were used to test differences in two sub-study subjects
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BMC Pregnancy and Childbirth

ISSN: 1471-2393

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