| Total (n = 3830) | Level of education | Overall p value* | |||||||||
| High (n = 1264) | Mid–high (n = 955) | Mid–low (n = 973) | Low (n = 638) | ||||||||
| Pregnancy characteristics | |||||||||||
| Pregnant women’s age (years) | 31.3 (4.5) | 33.0 (3.1) | 32.0 (3.7) | 30.1 (4.7) | 28.6 (5.5) | <0.001 | |||||
| Pregnant women’s height (cm) | 170.8 (6.4) | 171.5 (6.1) | 171.4 (6.3) | 170.6 (6.4) | 168.9 (6.7) | <0.001 | |||||
| Preeclampsia (% yes) | 1.9 | 1.2 | 1.1 | 2.5 | 3.6 | <0.001 | |||||
| IUGR (% yes) | 1.4 | 0.9 | 1.2 | 1.7 | 2.3 | 0.076 | |||||
| Parity (% primipara) | 59.8 | 56.9 | 61.5 | 63.8 | 55.7 | <0.001 | |||||
| Infant gender (% girls) | 49.9 | 49.6 | 49.4 | 51.6 | 48.5 | 0.631 | |||||
| Psychosocial factors | |||||||||||
| Marital status (% single) | 7.6 | 3.3 | 4.2 | 8.2 | 20.1 | <0.001 | |||||
| Pregnancy planning (% not planned) | 18.5 | 10.1 | 16.0 | 21.6 | 34.0 | <0.001 | |||||
| Financial concerns | |||||||||||
| No concerns (%) | 88.4 | 95.5 | 91.1 | 85.8 | 69.7 | <0.001 | |||||
| Some concerns (%) | 10.4 | 4.3 | 8.2 | 13.2 | 25.2 | ||||||
| Great concerns (%) | 1.2 | 0.3 | 0.7 | 1.1 | 5.0 | ||||||
| Long-lasting difficulties (score) | 1.08 (1.0–2.9) | 1.08 (1.0–2.6) | 1.08 (1.0–2.3) | 1.09 (1.0–2.6) | 1.17 (1.0–2.9) | <0.001 | |||||
| Psychopathology (score) | 0.12 (0.0–3.0) | 0.10 (0.0–2.2) | 0.12 (0.0–1.7) | 0.13 (0.0–3.0) | 0.17 (0.0–2.6) | <0.001 | |||||
| Working hours (hours) | 27.4 (13.6) | 32.5 (10.8) | 27.9 (11.9) | 25.1 (14.0) | 17.6 (15.8) | <0.001 | |||||
| Lifestyle habits | |||||||||||
| Smoking | |||||||||||
| No (%) | 73.4 | 87.1 | 78.6 | 69.4 | 46.1 | <0.001 | |||||
| Until pregnancy known (%) | 9.0 | 7.8 | 9.7 | 10.1 | 8.8 | ||||||
| Continued during pregnancy (%) | 17.5 | 5.1 | 11.7 | 20.6 | 45.1 | ||||||
| Alcohol consumption | |||||||||||
| No (%) | 50.2 | 32.4 | 45.2 | 64.0 | 74.9 | <0.001 | |||||
| <1 drink per week (%) | 34.0 | 43.4 | 37.2 | 26.9 | 19.9 | ||||||
| 1–6 drinks per week (%) | 14.8 | 23.5 | 15.6 | 8.6 | 4.7 | ||||||
| ⩾1 drink per day (%) | 1.0 | 0.7 | 1.9 | 0.5 | 0.5 | ||||||
| BMI (kg/m2) | |||||||||||
| <18 (%) | 0.7 | 0.6 | 0.4 | 0.7 | 1.1 | <0.001 | |||||
| 18–25 (%) | 66.7 | 75.4 | 72.7 | 60.0 | 50.8 | ||||||
| >25 (%) | 32.6 | 24.0 | 26.9 | 39.3 | 48.1 | ||||||
| Outcome | |||||||||||
| Gestational duration | |||||||||||
| ⩾37 weeks | 95.2 | 95.6 | 95.9 | 96.2 | 92.0 | 0.002 | |||||
| 34–36 weeks | 3.6 | 3.4 | 3.4 | 2.7 | 5.5 | ||||||
| <34 weeks | 1.2 | 1.0 | 0.7 | 1.1 | 2.5 | ||||||
| OR preterm birth (<37 weeks)† (95% CI) | Reference | 0.89 (0.59 to 1.36) | 0.82 (0.54 to 1.26) | 1.89 (1.28 to 2.80) | |||||||
Values are means (SD) for continuous normally distributed variables, medians (100% range) for continuous non-normally distributed variables, and percentages for categorical variables, for the total population and by level of education.
Due to the small number of women (n = 35) in the category “⩾1 drink per day”, this category was merged with the category “1–6 drinks per week” in all other analyses.
*ANOVA for continuous normally distributed variables, Kruskal–Wallis test for continuous non-normally distributed variables, and χ2 test for categorical variables.
†Adjusted for parity of the pregnant woman and gender of the child.
BMI, body mass index; IUGR, intrauterine growth restriction.