Introduction
Methods
Data
Population
Variables and definitions
Individual level information
Residential area level information
Statistical analyses
Ethics approval
Results
Characteristic | Preterm birth (<37weeks) | Term (<37weeks) | *pvalue | SGA (<2 SD) | Not SGA | *pvalue |
---|---|---|---|---|---|---|
Individual level information | ||||||
n (%) | 15,615 (4.5) | 330,337 | 13,111 (3.8) | 332,626 | ||
Mean maternal age, years (SD) | 29.8 (5.7) | 29.5 (5.4) | ≤0.001 | 29.1 (5.9) | 29.5 (5.4) | ≤0.001 |
Maternal age, years %
| ≤0.001 | ≤0.001 | ||||
<20 | 5.7 | 94.3 | 6.6 | 93.4 | ||
20-29 | 4.3 | 95.7 | 3.9 | 96.1 | ||
30-39 | 4.5 | 95.5 | 3.5 | 96.5 | ||
40 or more | 6.1 | 93.9 | 4.7 | 95.3 | ||
Prior preterm birth
| ≤0.001 | 0.016 | ||||
Yes | 14.5 | 85.5 | 4.2 | 95.8 | ||
No | 3.8 | 96.2 | ||||
Parity %
| ≤0.001 | |||||
Nulliparous women | 5.3 | 94.7 | ≤0.001 | 6.2 | 93.8 | |
Multiparous women | 3.9 | 96.1 | 2.1 | 97.9 | ||
Smoking status
| ≤0.001 | |||||
Non-smoking | 4.3 | 95.7 | 3.3 | 96.7 | ||
Quit smoking during 1st trimester | 4.5 | 95.5 | 3.7 | 96.3 | ||
Smoking after 1st trimester | 5.6 | 94.4 | 7.5 | 92.5 | ||
Missing information | 8.2 | 91.8 | 3.8 | 96.2 | ||
Socioeconomic status %
| ≤0.001 | ≤0.001 | ||||
Upper white collar workers | 4.0 | 96.0 | 3.2 | 96.8 | ||
Lower white collar workers | 4.5 | 95.5 | 3.6 | 96.4 | ||
Blue collar workers | 4.7 | 95.3 | 4.1 | 95.9 | ||
Othersa | 4.3 | 95.7 | 3.8 | 96.2 | ||
Missing information | 4.9 | 95.1 | 4.1 | 95.9 | ||
Year
| 0.531 | 0.017 | ||||
2005 | 4.5 | 95.5 | 3.7 | 96.3 | ||
2006 | 4.7 | 95.3 | 3.6 | 96.4 | ||
2007 | 4.5 | 95.5 | 4.0 | 96.0 | ||
2008 | 4.5 | 95.5 | 3.7 | 96.3 | ||
2009 | 4.4 | 95.6 | 3.9 | 96.1 | ||
2010 | 4.5 | 95.5 | 3.8 | 96.2 | ||
Municipality level information | ||||||
Education deprivation class
| 0.003 | 0.116 | ||||
High (least deprived) | 4.3 | 95.7 | 3.8 | 96.2 | ||
Intermediate | 4.6 | 95.4 | 3.9 | 96.1 | ||
Low (most deprived) | 4.6 | 95.4 | 3.7 | 96.3 | ||
Income deprivation class
| ≤0.001 | 0.574 | ||||
High (least deprived) | 4.3 | 95.7 | 3.8 | 96.2 | ||
Intermediate | 4.6 | 95.4 | 3.7 | 96.3 | ||
Low (most deprived) | 4.6 | 95.4 | 3.8 | 96.2 | ||
Unemployment deprivation class
| ≤0.001 | ≤0.001 | ||||
Low (least deprived) | 4.3 | 95.7 | 3.7 | 96.3 | ||
Intermediate | 4.6 | 95.4 | 3.7 | 96.3 | ||
High (most deprived) | 4.7 | 95.3 | 4.0 | 96.0 | ||
Tertiles of municipality by population size
| ≤0.001 | 0.04 | ||||
First tertile (100-21,000) | 3.5 | 96.5 | 4.5 | 95.5 | ||
Second tertile (21,000-106,000) | 3.9 | 96.1 | 4.6 | 95.4 | ||
Third tertile (106,000-600,000) | 3.9 | 96.1 | 4.4 | 95.6 |
Characteristics | Model 1 adjusted for year of birth | Model 2 adjusted for individual level confounders | Model 3 adjusted for municipality level confounders | Model 4 adjusted for model 2 (except smoking) and Model 3 | Model 5 adjusted for model 2 and model 3 |
---|---|---|---|---|---|
OR (95% CI) | aOR (95% CI) | aOR (95% CI) | aOR (95% CI) | aOR (95% CI) | |
Year of birth | 0.99 (0.99-1.00) | 0.99 (0.98-1.00) | 0.99 (0.98-1.00) | 0.99 (0.98-1.00) | |
Maternal age, years (per one year increase) | 1.02 (1.02-1.03) | 1.02 (1.02-1.02) | 1.02 (1.02-1.03) | ||
Parity
| |||||
Nulliparous women | 1 | 1 | 1 | ||
Multiparous women | 0.52 (0.50-0.54) | 0.52 (0.50-0.54) | 0.51 (0.49-0.53) | ||
Prior preterm birth | 5.28 (5.00-5.57) | 5.30 (5.03-5.59) | 5.27 (4.99-5.56) | ||
Smoking status
| |||||
Non-smoking | 1 | 1 | |||
Quit smoking during 1st trimester | 1.03 (0.95-1.12) | 1.03 (0.95-1.11) | |||
Smoking after 1st trimester | 1.36 (1.29-1.43) | 1.35 (1.29-1.42) | |||
Missing information | 2.05 (1.89-2.22) | 2.02 (1.86-2.19) | |||
Socioeconomic status
| |||||
Upper white collar workers | 1 | 1 | 1 | ||
Lower white collar workers | 1.15 (1.07-1.23) | 1.15 (1.07-1.23) | 1.13 (1.06-1.21) | ||
Blue collar workers | 1.19 (1.11-1.29) | 1.23 (1.14-1.33) | 1.18 (1.09-1.27) | ||
Othersa | 1.11 (1.03-1.19) | 1.12 (1.05-1.20) | 1.10 (1.03-1.18) | ||
Missing information | 1.27 (1.14-1.32) | 1.27 (1.18-1.36) | 1.24 (1.15-1.33) | ||
Municipality derivation class
b
| |||||
Education
| |||||
High (least deprived) | 1 | 1 | 1 | ||
Intermediate | 1.05 (1.00-1.10) | 1.06 (1.01-1.11) | 1.06 (1.01-1.11) | ||
Low (most deprived) | 1.03 (0.97-1.10) | 1.03 (0.97-1.10) | 1.03 (0.96-1.10) | ||
Income
| |||||
High (least deprived) | 1 | 1 | 1 | ||
Intermediate | 1.03 (0.98-1.09) | 1.05 (0.99-1.11) | 1.05 (0.99-1.11) | ||
Low (most deprived) | 1.05 (0.98-1.12) | 1.07 (1.00-1.14) | 1.06 (0.99-1.14) | ||
Unemployment
| |||||
Low (least deprived) | 1 | 1 | 1 | ||
Intermediate | 1.02 (0.98-1.07) | 1.03 (0.98-1.08) | 1.02 (0.98-1.08) | ||
High (most deprived) | 1.04 (0.99-1.10) | 1.05 (1.00-1.11) | 1.05 (0.99-1.11) | ||
Log (population) | 1.01 (0.99-1.02) | 1.00 (0.98-1.01) | 1.00 (0.98-1.02) |
Characteristic | Model 1 adjusted for year of birth | Model 2 adjusted for individual level confounders | Model 3 adjusted for municipality level confounders | Model 4 adjusted for model 2 (except smoking) and Model 3 | Model 5 adjusted for model 2 and model 3 |
---|---|---|---|---|---|
OR (95% CI) | aOR (95% CI) | aOR (95% CI) | aOR (95% CI) | aOR (95% CI) | |
Year of birth | 1.01 (1.00-1.02) | 1.01 (1.00-1.02) | 1.01 (1.00-1.02) | 1.01 (1.00-1.02) | |
Maternal age, years (per one year increase) | 1.03 (1.03-1.04) | 1.02 (1.02-1.03 | 1.03 (1.03-1.04) | ||
Parity
| |||||
Nulliparous women | 1 | 1 | 1 | ||
Multiparous women | 0.27 (0.26-0.28) | 0.27 (0.26-0.28) | 0.27 (0.25-0.28) | ||
Prior preterm birth | 2.14 (1.96-2.34) | 2.20 (2.01-2.40) | 2.14 (1.96-2.34) | ||
Smoking status
| |||||
Non-smoking | 1 | 1 | |||
Quit smoking during 1st trimester | 0.96 (0.88-1.05) | 0.96 (0.88-1.05) | |||
Smoking after 1st trimester | 2.47 (2.35-2.59) | 2.45 (2.34-2.57) | |||
Missing information | 1.34 (1.19-1.49) | 1.32 (1.18-1.48) | |||
Socioeconomic status
| |||||
Upper white collar workers | 1 | 1 | 1 | ||
Lower white collar workers | 1.179 (1.09-1.26) | 1.22 (1.13-1.31) | 1.16 (1.08-1.25) | ||
Blue collar workers | 1.21 (1.11-1.32) | 1.39 (1.28-1.51) | 1.20 (1.10-1.30) | ||
Othersa | 1.17 (1.09-1.27) | 1.23 (1.14-1.32) | 1.17 (1.08-1.26) | ||
Missing information | 1.19 (1.10-1.29) | 1.29 (1.20-1.40) | 1.20 (1.111.29) | ||
Municipality derivation class
b
| |||||
Education
| |||||
High (least deprived) | 1 | 1 | 1 | ||
Intermediate | 1.09 (1.03-1.14) | 1.07 (1.01-1.13) | 1.03 (0.98-1.09) | ||
Low (most deprived) | 1.12 (1.04-1.20) | 1.11 (1.03-1.19) | 1.05 (0.97-1.13) | ||
Income
| |||||
High (least deprived) | 1 | 1 | 1 | ||
Intermediate | 0.94 (0.88-0.99) | 0.93 (0.87-0.99) | 0.94 (0.89-1.00) | ||
Low (most deprived) | 0.99 (0.92-1.07) | 0.99 (0.92-1.07) | 1.01 (0.94-1.09) | ||
Unemployment
| |||||
Low (least deprived) | 1 | 1 | 1 | ||
Intermediate | 1.03 (0.98-1.09) | 1.07 (1.01-1.12) | 1.06 (1.01-1.12) | ||
High (most deprived) | 1.12 (1.06-1.19) | 1.15 (1.08-1.22) | 1.13 (1.06-1.20) | ||
Log (population) | 1.06 (1.04-1.08) | 1.01 (1.00-1.03) | 1.01 (0.99-1.03) |
Characteristics | Preterm birth | SGA |
---|---|---|
aOR (95% CI) | aOR (95% CI) | |
Year of birth | 1.00 (0.99-1.01) | 1.01 (1.00-1.02) |
Maternal age, years (per one year increase) | 1.02 (1.02-1.03) | 1.04 (1.03-1.04) |
Parity
| ||
Nulliparous women | 1 | 1 |
Multiparous women | 0.52 (0.50-0.54) | 0.26 (0.25-0.28) |
Prior preterm birth | 5.27 (4.99-5.55) | 2.14 (1.96-2.34) |
Smoking status
| ||
Non-smoking | 1 | 1 |
Quit smoking during 1st trimester | 1.03 (0.95-1.11) | 0.95 (0.87-1.03) |
Smoking after 1st trimester | 1.37 (1.30-1.43) | 2.45 (2.33-2.56) |
Socioeconomic status
| ||
Upper white collar workers | 1 | 1 |
Lower white collar workers | 1.13 (1.06-1.19) | 1.18 (1.11-1.27) |
Blue collar workers | 1.20 (1.12-1.28) | 1.21 (1.13-1.31) |
Othersa | 1.09 (1.02-1.16) | 1.18 (1.10-1.27) |
Municipality derivation class
b
| ||
Education
| ||
High (least deprived) | 1 | 1 |
Intermediate | 1.04 (0.99-1.09) | 1.02 (0.97-1.08) |
Low (most deprived) | 1.01 (0.95-1.08) | 1.04 (0.97-1.12) |
Income
| ||
High (least deprived) | 1 | 1 |
Intermediate | 1.04 (0.99-1.10) | 0.94 (0.88-1.00) |
Low (most deprived) | 1.06 (0.99-1.14) | 1.00 (0.93-1.08) |
Unemployment
| ||
Low (least deprived) | 1 | 1 |
Intermediate | 1.03 (0.98-1.08) | 1.07 (1.01-1.12) |
High (most deprived) | 1.04 (0.98-1.08) | 1.13 (1.06-1.20) |
Log (population) | 1.00 (0.98-1.01) | 1.01 (0.99-1.03) |