Table 3.
Associations between maternal characteristics and risks of indicated preterm (<37 weeks) and early-term birth (37–38 weeks) using births reaching full term (ie, 39 weeks and over, n=10 269) as the reference in a representative sample of births in France in 2010
| <37 weeks GA % | 37–38 weeks GA % | P value* | <37 weeks GA | 95% CI | 37–38 weeks GA | 95% CI | |
| n=374 | n=1259 | aRRRs | aRRRs | ||||
| Maternal age (years) | |||||||
| <20 | 4.1 | 1.9 | 0.0000 | 1.1 | 0.6 to 2.0 | 0.9 | 0.6 to 1.4 |
| 20–24 | 13.5 | 11.9 | 0.8 | 0.6 to 1.1 | 0.9 | 0.8 to 1.2 | |
| 25–29 | 30.5 | 27.6 | Ref. | – | Ref. | – | |
| 30–34 | 31.6 | 30.1 | 1.3 | 1.0 to 1.7 | 1.2 | 1.0 to 1.4 | |
| ≥35 | 20.3 | 28.4 | 1.4 | 1.0 to 1.9 | 1.8 | 1.5 to 2.1 | |
| Parity | |||||||
| 1 | 51.5 | 36.6 | 0.0000 | 2.1 | 1.6 to 2.7 | 1.0 | 0.9 to 1.2 |
| 2–3 | 38.8 | 50.3 | Ref. | – | Ref. | – | |
| 4 | 9.7 | 13.2 | 1.1 | 0.7 to 1.6 | 1.3 | 1.1 to 1.6 | |
| Previous preterm birth | |||||||
| Yes | 89.0 | 93.5 | 0.0000 | 6.6 | 4.5 to 9.7 | 2.5 | 1.9 to 3.3 |
| No | 11.0 | 6.5 | Ref. | – | Ref. | – | |
| Maternal height (cm) | |||||||
| Q1: 100–160 | 37.2 | 36.9 | 0.0000 | 1.3 | 1.0 to 1.8 | 1.5 | 1.3 to 1.8 |
| Q2: 161–165 | 25.2 | 29.3 | 1.0 | 0.7 to 1.3 | 1.2 | 1.0 to 1.5 | |
| Q3: 166–168 | 15.9 | 14.4 | 1.0 | 0.7 to 1.4 | 1.0 | 0.8 to 1.3 | |
| Q4: 169–190 | 21.6 | 19.3 | Ref. | – | Ref. | – | |
| Prepregnancy BMI† | |||||||
| <18.5 | 10.4 | 5.6 | 0.0000 | 1.4 | 1.0 to 2.1 | 0.8 | 0.6 to 1.1 |
| 18.5–24.9 | 57.7 | 58.3 | Ref. | – | Ref. | – | |
| 25–29.9 | 17.6 | 19.6 | 1.0 | 0.8 to 1.4 | 1.1 | 0.9 to 1.3 | |
| ≥30 | 14.4 | 16.5 | 1.6 | 1.1 to 2.2 | 1.7 | 1.4 to 2.0 | |
| Nationality | |||||||
| French | 84.2 | 84.9 | 0.0044 | Ref. | – | Ref. | – |
| Other Europe | 2.9 | 2.8 | 0.8 | 0.4 to 1.6 | 0.8 | 0.6 to 1.2 | |
| North African | 4.1 | 5.1 | 0.8 | 0.5 to 1.5 | 0.9 | 0.7 to 1.2 | |
| Sub-Saharan Africa | 5.9 | 4.6 | 2.2 | 1.4 to 3.5 | 1.6 | 1.2 to 2.2 | |
| Other | 2.9 | 2.6 | 1.2 | 0.6 to 2.2 | 1.1 | 0.8 to 1.6 | |
| Level of education | |||||||
| Low ISCED 0–2 | 38.0 | 34.2 | 0.0000 | 2.0 | 1.5 to 2.8 | 1.5 | 1.3 to 1.8 |
| Medium ISCED 3–5 | 39.4 | 42.0 | 1.4 | 1.0 to 1.8 | 1.3 | 1.1 to 1.5 | |
| High ISCED 6+ | 22.7 | 23.8 | Ref. | – | Ref. | – | |
| Smoking (number of cigarettes/day during the third trimester) | |||||||
| 0 | 80.5 | 80.3 | 0.0068 | Ref. | – | Ref. | – |
| 1–9 | 14.1 | 14.1 | 1.1 | 0.8 to 1.5 | 1.2 | 1.0 to 1.4 | |
| ≥10 | 5.4 | 5.6 | 1.0 | 0.6 to 1.6 | 1.1 | 0.9 to 1.5 | |
Ref. indicates the reference category for each variable.
*F-test.
†BMI. Body mass index in kg/m2.
aRRR, adjusted relative risk ratio; BMI, body mass index; GA, gestational age; ISCED 2011, International Standard Classification of Education 2011.