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Table 1 Cohort characteristics. Values are mean (SD), median (min-max) or n (%)

From: Persistent organic pollutants, pre-pregnancy use of combined oral contraceptives, age, and time-to-pregnancy in the SELMA cohort

Characteristic Total Cohort (n = 818) <  29 years old p-value* ≥ 29 years old p-value*
Non-COC user
(n = 164)
COC user
(n = 173)
Non-COC user
(n = 280)
COC user
(n = 201)
Time to Pregnancy, months, median (min-max) 3 (0–84) 2 (0–48) 3 (0–36) 0.008 2 (0–84) 4 (0–84) < 0.001
Age, yr, mean (SD) 29 (4.5) 25 (2.4) 25.5 (2.6) 0.03 32.9 (3.0) 31.7 (2.4) < 0.001
Pre-pregnancy combined oral contraceptive use, n (%) 374 (45.7) 173   201
Parity, median (min-max) 0 (0–5) 0 (0–3) 0 (0–2) < 0.001 1 (0–5) 0 (0–5) < 0.001
Maternal BMI, kg/m2, median (min-max) 23.7 (16.9–45.4) 23.8 (17.3–40.1) 23.3 (17.2–39.3) 0.25 24.1 (16.9–45.4) 23.7 (18.3–39.8) 0.83
Paternal BMI, kg/m2, median (min-max) 25.6 (18.7–44.0) 25.4 (19.4–44.0) 25.5 (18.7–40.4) 0.98 25.7 (19.4–39.9) 25.8 (19.6–35.9) 0.96
Regularity of menses, n (%) Regular 695 (85.0) 131 (79.9) 152 (87.9) 0.06 250 (89.3) 162 (80.6) 0.01
Irregular 123 (15.0) 33 (20.1) 21 (12.1) 30 (10.7) 39 (19.4)
Smoking, n (%) Non smoker (Cotinine 0–0.2 ng/mL) 739 (90.3) 143 (87.2) 159 (91.9) 0.33 250 (89.3) 187 (93) 0.37
Passive smoker (Cotinine 0.2–15 ng/mL) 38 (4.6) 9 (5.5) 7 (4) 15 (5.4) 7 (3.5)
Active smoker (Cotinine > 15 ng/mL) 41 (5.0) 12 (7.3) 7 (4) 15 (5.4) 7 (3.5)
Alcohol, n (%) Never 84 (10.3) 28 (17.1) 14 (8.1) 0.07 30 (10.7) 12 (6) 0.26
Seldom 359 (43.9) 80 (48.8) 93 (53.8) 102 (36.4) 84 (41.8)
Once every other week 181 (22.1) 29 (17.7) 40 (23.1) 67 (23.9) 45 (22.4)
At least once a week 194 (23.7) 27 (16.5) 26 (15) 81 (28.9) 60 (29.9)
Physical activity, n (%) < 1 h/week 222 (27.1) 47 (28.7) 38 (22) 0.39 90 (32.1) 47 (23.4) 0.004
1 h/week 133 (16.3) 27 (16.5) 28 (16.2) 54 (19.3) 24 (11.9)
1–2 h/week 220 (26.9) 41 (25) 42 (24.3) 74 (26.4) 63 (31.3)
at least 3 h/week 243 (29.7) 49 (29.9) 65 (37.6) 62 (22.1) 67 (33.3)
Education, n (%) Elementary 11 (1.3) 5 (3.0) 1 (0.6) 0.20 3 (1.1) 2 (1.0) 0.99
High school/vocational 308 (37.7) 82 (50.0) 84 (48.6) 83 (29.6) 59 (29.4)
University/College 499 (61.0) 77 (47.0) 88 (50.9) 194 (69.3) 140 (69.7)
  1. Abbreviation: BMI body mass index, COC combined oral contraceptive
  2. *Based on Wilcox, t.test or Chi-square test