Table 1 Baseline characteristics of the study population

All participants

191

65

95

81

Sociodemographic characteristics

 Age, years (mean ± SD)

31.55 ± 3.57

31.43 ± 3.56

31.60 ± 3.75

31.10 ± 3.23

0.51

0.47

  20–34

154 (80.63)

56 (86.15)

74 (77.89)

64 (79.01)

1.85

0.60

  35–49

37 (19.37)

9 (13.85)

21 (22.11)

17 (20.99)

  Missing

0

0

0

0

 Education level

  High school or below

28 (14.66)

14 (21.54)

12 (12.64)

12 (14.81)

-

0.24^a

  Bachelor degree

142 (74.35)

47 (72.31)

70 (73.68)

65 (80.25)

  Master degree or above

21 (10.99)

4 (6.15)

13 (13.68)

4 (4.94)

  Missing

0

0

0

0

Health status/lifestyles

 BMI, kg/m² (mean ± SD)

21.25 ± 3.51

21.54 ± 2.89

21.17 ± 2.68

20.94 ± 2.81

0.51

0.48

  Underweight (< 18.50)

24 (12.57)

11 (16.92)

14 (14.74)

12 (14.81)

5.35

0.50

  Normal (18.50–23.90)

144 (75.39)

40 (61.54)

65 (68.42)

57 (70.37)

  Overweight and obesity (≥ 24.00)

23 (12.04)

14 (21.54)

16 (16.84)

12 (14.82)

  Missing

0

0

0

0

 Hypertension

  Yes

1 (0.52)

1 (1.54)

2 (2.11)

3 (3.70)

-

0.19^a

  No

190 (99.48)

64 (98.46)

93 (97.89)

78 (96.30)

  Missing

0

0

0

0

 Tobacco exposure

  Yes

2 (1.06)

0 (0.00)

8 (8.51)

0 (0.00)

-

< 0.01^a

  No

187 (98.94)

63 (100.00)

86 (91.49)

81 (100.00)

  Missing

2

2

1

0

 Alcohol intake

  Yes

18 (9.42)

8 (12.31)

21 (22.11)

5 (6.17)

12.96

< 0.01

  No

173 (90.58)

57 (87.69)

74 (77.89)

76 (93.83)

  Missing

0

0

0

0

Menstrual/reproduction history

 Regular menstruation

  Yes

177 (92.67)

59 (90.77)

83 (87.37)

75 (92.59)

2.46

0.48

  No

14 (7.33)

6 (9.23)

12 (12.63)

6 (7.41)

  Missing

0

0

0

0

 Number of gestation

  1

116 (60.73)

38 (58.46)

64 (67.37)

58 (71.60)

4.24

0.24

  ≥ 2

75 (39.27)

27 (41.54)

31 (32.63)

23 (28.40)

  Missing

0

0

0

0

 Number of parturition

  0

72 (37.70)

22 (33.85)

36 (37.89)

38 (46.91)

3.04

0.38

  ≥ 1

119 (62.30)

43 (66.15)

59 (62.11)

43 (53.09)

  Missing

0

0

0

0