Table 3.
Co-sibling analyses for gestational age at birth in relation to asthma risk, Sweden, 1973–2018.
| Gestational age at birth | Cases | HR (95% CI)a |
|---|---|---|
| Attained ages up to 46 years | ||
| Preterm (<37 wks) | 31,945 | 1.40 (1.38, 1.43) |
| Extremely preterm (22–27 wks) | 1,417 | 3.28 (2.95, 3.64) |
| Very or moderately preterm (28–33 wks) | 7,416 | 1.79 (1.72, 1.86) |
| Late preterm (34–36 wks) | 23,112 | 1.28 (1.25, 1.31) |
| Early term (37–38 wks) | 101,100 | 1.09 (1.08, 1.11) |
| Full-term (39–41 wks) | 349,147 | Reference |
| Post-term (≥42 wks) | 38,358 | 0.99 (0.97, 1.00) |
| Per additional week (trend) | 0.95 (0.95, 0.95) | |
| Attained ages <10 years | ||
| Preterm (<37 wks) | 19,931 | 1.72 (1.67, 1.76) |
| Extremely preterm (22–27 wks) | 1,192 | 4.50 (3.97, 5.10) |
| Very or moderately preterm (28–33 wks) | 5,069 | 2.38 (2.26, 2.51) |
| Late preterm (34–36 wks) | 13,670 | 1.50 (1.46, 1.55) |
| Early term (37–38 wks) | 57,290 | 1.15 (1.13, 1.17) |
| Full-term (39–41 wks) | 180,163 | Reference |
| Post-term (≥42 wks) | 17,611 | 0.97 (0.94, 0.99) |
| Per additional week (trend) | 0.92 (0.92, 0.92) | |
| Attained ages 10–17 years | ||
| Preterm (<37 wks) | 5,266 | 1.21 (1.17, 1.26) |
| Extremely preterm (22–27 wks) | 110 | 1.74 (1.42, 2.11) |
| Very or moderately preterm (28–33 wks) | 1,052 | 1.40 (1.30, 1.51) |
| Late preterm (34–36 wks) | 4,104 | 1.16 (1.11, 1.21) |
| Early term (37–38 wks) | 20,476 | 1.05 (1.03, 1.07) |
| Full-term (39–41 wks) | 75,513 | Reference |
| Post-term (≥42 wks) | 7,991 | 1.01 (0.98, 1.04) |
| Per additional week (trend) | 0.97 (0.97, 0.98) | |
| Attained ages 18–46 years | ||
| Preterm (<37 wks) | 10,478 | 1.13 (1.09, 1.17) |
| Extremely preterm (22–27 wks) | 233 | 1.37 (1.09, 1.71) |
| Very or moderately preterm (28–33 wks) | 2,170 | 1.24 (1.16, 1.34) |
| Late preterm (34–36 wks) | 8,075 | 1.10 (1.06, 1.15) |
| Early term (37–38 wks) | 34,902 | 1.04 (1.02, 1.07) |
| Full-term (39–41 wks) | 133,729 | Reference |
| Post-term (≥42 wks) | 17,075 | 0.99 (0.96, 1.01) |
| Per additional week (trend) | 0.98 (0.98, 0.98) |
a
Adjusted for shared familial (genetic and/or environmental) factors, in addition to child characteristics (birth year, sex, birth order), maternal characteristics (age, education, smoking, BMI, asthma), and paternal characteristics (age, education, asthma).