Introduction
Methods
Study design, population, and data sources
Exposure variable
Outcome measures
Covariates
Mediators
Statistical analyses
Mediation analysis
Results
Characteristics | N | % |
---|---|---|
All births
| 258,005 | 100 |
Maternal age (years)
| ||
<20 | 7012 | 2.7 |
20–24 | 29 983 | 11.6 |
25–29 | 71,571 | 27.7 |
30–34 | 92,040 | 35.7 |
35–40 | 50,852 | 19.7 |
≥41 | 6528 | 2.5 |
Missing | 19 | 0 |
Smoking during pregnancy
| ||
No | 229,007 | 88.7 |
Yes | 21,326 | 8.3 |
Missing | 7672 | 3.0 |
Neighbourhood income quintile
| ||
1 (lowest) | 55,701 | 21.6 |
2 | 51,333 | 19.9 |
3 | 51,866 | 20.1 |
4 | 54,961 | 21.3 |
5 (highest) | 41,856 | 16.2 |
Missing | 2288 | 0.9 |
Pre-pregnancy BMI (kg/m
2
)
| ||
<18.5 (underweight) | 10,901 | 4.2 |
18.5–24.9 (normal) | 108,170 | 41.9 |
25-29.9 (overweight) | 48,141 | 18.7 |
≥30 (obese) | 36,950 | 14.3 |
Missing | 53,843 | 20.9 |
Maternal weight gain during pregnancy
| ||
Below recommended | 42,826 | 16.6 |
Recommended | 54,302 | 21 |
Above recommended | 73,999 | 28.7 |
Missing | 86,878 | 33.7 |
Infant sex
| ||
Male | 132,231 | 51.3 |
Female | 125,629 | 48.7 |
Missing | 145 | 0.0 |
Gestational age at birth (weeks)
| ||
<37 | 15,211 | 5.9 |
≥37 | 242,794 | 94.1 |
Birth weight (grams)
| ||
<2500 | 11,762 | 4.6 |
≥2500 | 246,243 | 95.4 |
SGA
| ||
No | 234,120 | 90.7 |
Yes | 23,653 | 9.2 |
Missing | 232 | 0.09 |
Mediation analysis results for pre-pregnancy BMI
Step 1 (relationship between exposure and outcome)
Step 2 (relationship between exposure and mediator)
Step 3 (relationship between the mediator and outcome)
Step 4 (relationship of the exposure and mediators to the outcome)
SGA [Beta Estimate (95% CI)] | % Mediated | |||||||
---|---|---|---|---|---|---|---|---|
Total Effect | Direct Effect | Indirect Effect | ||||||
Unadjusted | Adjusted* | Unadjusted | Adjusted* | Unadjusted | Adjusted* | Unadjusted | Adjusted* | |
Hospitalizations
| ||||||||
Overweight | 0.02 (0.01, 0.03) | 0.02 (0.01, 0.03) | 0.02 (0.02, 0.03) | 0.02 (0.01, 0.03) | 0.00 (0.00–0.00) | 0.00 (0.00–0.00) | ** | ** |
Obese | 0.05 (0.04, 0.06) | 0.05 (0.04, 0.05) | 0.05 (0.04, 0.06) | 0.05 (0.04, 0.06) | 0.00 (0.00–0.00) | 0.00 (0.00–0.00) | ** | ** |
Mediation analysis results for GWG
Step 2 (relationship between exposure and mediator)
Step 3 (relationship between the mediator and outcome)
Step 4 (relationship of the exposure and mediators to the outcome)
[Beta Estimate (95% CI)] | % Mediated | |||||||
---|---|---|---|---|---|---|---|---|
Total Effect | Direct Effect | Indirect Effect | ||||||
Unadjusted | Adjusted* | Unadjusted | Adjusted* | Unadjusted | Adjusted* | Unadjusted | Adjusted* | |
Hospitalizations, mediated by PTB
| ||||||||
Below recommended | 0.02 (0.01, 0.03) | 0.02 (0.01, 0.03) | 0.01 (0.00, 0.02) | 0.01 (0.00, 0.02) | 0.01 (0.01, 0.01) | 0.01 (0.01, 0.01) | 54.6 | 56.7 |
Hospitalizations, mediated by SGA
| ||||||||
Below recommended | 0.02 (0.01, 0.03) | 0.02 (0.01, 0.03) | 0.02 (0.01, 0.03) | 0.02 (0.01, 0.03) | 0.00 (0.00, 0.00) | 0.00 (0.00, 0.00) | 7.3 | 6.8 |