Table 1. Distribution of covariates in relation to maternal smoking status.
| Maternal smoking | No smoking | Smoking only during pregnancy | Smoking only postnatally | Smoking during pregnancy and postnatally | ||||||
| n = 25,076 | n = 3,343 | n = 140 | n = 4,188 | |||||||
| % | ±SD | % | ±SD | % | ±SD | % | ±SD | p-value* | ||
| 76.6 | 10.2 | 0.4 | 12.8 | |||||||
| Birth weight (g) | Mean | 3.688 | ±486 | 3.658 | ±507 | 3.714 | ±507 | 3.456 | ±494 | |
| <2,500 | 0.5 | 1.1 | 0.7 | 1.9 | <0.001 | |||||
| 2,500–4,000 | 73.0 | 73.5 | 72.2 | 83.6 | ||||||
| >4,000 | 26.5 | 25.4 | 27.1 | 14.5 | ||||||
| Parity | Primiparous | 44.2 | 57.4 | 37.9 | 42.6 | <0.001 | ||||
| Multiparous | 55.8 | 42.6 | 62.1 | 57.4 | ||||||
| Sex | Boy | 51.6 | 50.0 | 49.3 | 49.5 | 0.027 | ||||
| Girl | 48.4 | 50.0 | 50.7 | 50.5 | ||||||
| Breast feeding (weeks) | Mean | 16.8 | ±6.8 | 15.2 | ±7.7 | 17.6 | ±5.7 | 14.4 | ±7.3 | |
| None | 4.0 | 8.3 | 4.3 | 3.4 | <0.001 | |||||
| <14 | 17.1 | 22.6 | 9.4 | 34.1 | ||||||
| 14–22 | 63.4 | 56.5 | 72.6 | 52.9 | ||||||
| >22 | 15.5 | 12.6 | 13.7 | 9.6 | ||||||
| Maternal age (years) | Mean | 30.9 | ±4.1 | 30.0 | ±4.2 | 30.1 | ±3.7 | 30.5 | ±4.6 | |
| 16–25 | 6.0 | 11.2 | 7.2 | 11.3 | <0.001 | |||||
| 25–29.99 | 38.0 | 41.7 | 45.0 | 35.7 | ||||||
| 30–34.99 | 39.8 | 34.9 | 36.4 | 35.8 | ||||||
| ≥35 | 16.2 | 12.2 | 11.4 | 17.2 | ||||||
| Socio-occupational status | High | 73.6 | 66.9 | 77.2 | 51.7 | <0.001 | ||||
| Middel | 24.2 | 29.7 | 22.1 | 41.5 | ||||||
| Low | 2.2 | 3.4 | 0.7 | 6.8 | ||||||
| Maternal gestational Weight gain (kg) | Mean | 14.7 | ±5.1 | 17.3 | ±6.3 | 16.8 | ±6.3 | 15.1 | ±6.2 | |
| <10 | 12.2 | 7.7 | 7.9 | 15.9 | <0.001 | |||||
| 10–17.99 | 61.9 | 47.0 | 55.4 | 51.6 | ||||||
| ≥18 | 25.9 | 45.3 | 36.7 | 32.5 | ||||||
| Maternal pre-pregnancy BMI (kg/m2) | Mean | 23.4 | ±4.0 | 23.3 | ±4.1 | 22.8 | ±3.1 | 23.3 | ±4.1 | |
| <18.5 | 3.8 | 4.5 | 6.4 | 6.3 | <0.001 | |||||
| 18.5–24.9 | 70.8 | 70.4 | 69.8 | 67.7 | ||||||
| 25–29.9 | 18.5 | 18.5 | 20.9 | 18.6 | ||||||
| ≥30 | 6.8 | 6.5 | 2.9 | 7.4 | ||||||
| Paternal BMI (kg/m2) | Mean | 25.0 | ±3.7 | 25.3 | ±3.7 | 25.8 | ±4.1 | 25.3 | ±3.4 | |
| <18.5 | 0.4 | 0.2 | 0.0 | 0.3 | <0.001 | |||||
| 18.5–24.9 | 55.5 | 52.1 | 54.2 | 52.8 | ||||||
| 25–29.9 | 38.1 | 40.3 | 35.0 | 38.2 | ||||||
| ≥30 | 6.0 | 7.4 | 10.8 | 8.7 | ||||||
| Paternal smoking | No | 79.6 | 55.1 | 59.3 | 38.3 | <0.001 | ||||
| Yes | 20.4 | 44.9 | 40.7 | 61.7 | ||||||
Abbreviations: BMI: Body Mass Index. Missing information on variables; Parity (n = 16), maternal gestational weight gain (n = 284), maternal pre- pregnancy BMI (n = 453), socio-occupational status (n = 91), paternal smoking (n = 500), paternal BMI (n = 6,570) and breastfeeding (n = 8,998). * χ2-test.