Table 1 Baseline characteristics of study participants

Age (median years, IQR)

29 (26–35)

Age at menarche, years (%)

  ≤ 11

4.9

  12–13

44.8

  14–15

40.8

  ≥ 16

9.5

Time to regularity, years (%)

  ≤ 1

51.0

  2–4

21.2

  ≥ 5 or always irregular

27.8

Menstrual cycle regularity (%)

  Very regular

31.6

  Regular

44.3

  Usually irregular

17.6

  Always irregular

6.5

Menstrual cycle length, days (%)

  < 26

9.1

  26–31

59.2

  32–39

23.2

  ≥ 40 or too irregular to estimate

8.5

Parous (%)

31.5

    Age at first birth (median years, IQR)

30 (28–32)

    Duration of breastfeeding, ≥ 6 months (%)

50.1

Attempting to conceive, ≥ 1 year (%)

5.8

Oral contraceptives use, ≥ 2 months (%)

6.7

    Age at first use (median years, IQR)

26 (24–29)

Pap spear screening within past 2 years (%)

39.7

Ever smokers (%)

2.6

Alcohol consumption, ≥ 1 drink/day (%)

7.6

Body mass index, kg/m² (%)

  < 18.5

15.6

  18.5–22.9

66.7

  23–24.9

10.0

  ≥ 25

7.7

Perceived stress (scores, IQR)

7 (5–8)

Antihypertensive medication use (%)

0.5

Systolic blood pressure, mmHg (%)

  < 105

21.5

  105–114

41.4

  115–124

27.6

  125–134

7.9

  ≥ 135

1.6

Rotating night shift, nights/month (%)

  None

31.1

  < 7

36.8

  ≥ 7

32.1

On feet at work, hours/day (%)

  ≤ 4

33.4

  5–8

45.2

  ≥ 9

21.3