Table 2 Characteristics of primiparous women (N = 1089) and their offspring by the duration of breastfeeding
|  | <  6 months n = 329 | 6–11 months n = 569 | ≥ 12 months n = 191 | p for linearity |
|---|---|---|---|---|
Maternal characteristics | ||||
 Age (years), mean (SD) | 28.2 (5.6) | 29.0 (4.4) | 29.7 (4.4) | <  0.001 |
 Married, n (%) | 140 (43) | 305 (54) | 105 (55) | 0.002 |
 Smokers |  |  |  | <  0.001 |
  Non-smokers, n (%) | 262 (80) | 498 (88) | 171 (90) |  |
  Quitted during the first trimester, n (%) | 22 (7) | 44 (8) | 15 (8) |  |
  Smokers over pregnancy, n (%) | 45 (14) | 27 (5) | 5 (3) |  |
 Education years, mean (SD) | 13.0 (2.5) | 14.0 (2.4) | 14.5 (2.4) | <  0.001 |
 Annual maternal income (€), mean (SD) | 24,500 (14,100) | 27,000 (12,900) | 28,000 (12,400) | 0.002 |
 Pre-pregnancy body mass index (kg/m2), mean (SD) | 24.6 (4.8) | 23.5 (3.9) | 23.2 (3.7) | <  0.001 |
 Pregnancies without fertility treatments, n (%) | 303 (92) | 510 (90) | 170 (89) | 0.20 |
 Duration of pregnancy (weeks), mean (SD) | 39.8 (1.8) | 40.2 (1.4) | 40.0 (1.7) | 0.060 |
 Vaginal deliveries, n (%) | 258 (78) | 455 (80) | 156 (82) | 0.37 |
 Gestational diabetes mellitus, n (%) | 54 (16) | 80 (14) | 21 (11) | 0.088 |
 Chronic diseases | ||||
  Lung diseases, n (%) | 6 (2) | 15 (3) | 6 (3) | 0.33 |
  Rheumatoid diseases, n (%) | 3 (1) | 4 (1) | 2 (1) | 0.94 |
  Mental diseases, n (%) | 4 (1) | 3 (1) | 1 (1) | 0.30 |
  Thyroid diseases, n (%) | 0 (0) | 2 (0) | 0 (0) | 0.79 |
Infant characteristics | ||||
 Sex (boy), n (%) | 166 (50) | 292 (51) | 101 (53) | 0.60 |
 Birthweight (grams), mean (SD) | ||||
  Girls | 3373 (577) | 3390 (448) | 3348 (467) | 0.81 |
  Boys | 3527 (520) | 3529 (467) | 3540 (514) | 0.85 |
  Apgar score at 1 min, mean (SD) | 8.5 (1.4) | 8.5 (1.3) | 8.5 (1.2) | 0.61 |
  Admission to neonatal intensive care unit, n (%) | 35 (11) | 39 (7) | 17 (9) | 0.30 |
  Need for respirator treatment, n (%) | 11 (3) | 5 (1) | 3 (2) | 0.057 |