Table 2. Associations Between Gestational Age at Birth and Risk of Heart Failure, Sweden, 1973 Through 2015.
| Characteristica | Cases | Rateb | Hazard ratio (95% CI) | Unadjusted risk difference (95% CI)d | Weighted % | |||
|---|---|---|---|---|---|---|---|---|
| Unadjusted | Adjustedc | P value | AFee | PAFf | ||||
| Attained ages 0-43 y | ||||||||
| Preterm | 460 | 11.5 | 2.85 (2.58 to 3.15) | 2.69 (2.43 to 2.97) | <.001 | 7.4 (6.3 to 8.5) | 64.5 | 10.4 |
| Extremely preterm | 45 | 56.0 | 13.96 (10.39 to 18.75) | 12.83 (9.55 to 17.25) | <.001 | 51.9 (35.6 to 68.3) | 92.7 | 1.7 |
| Moderately preterm | 125 | 15.8 | 3.93 (3.28 to 4.70) | 3.65 (3.04 to 4.37) | <.001 | 11.7 (8.9 to 14.5) | 74.2 | 3.7 |
| Late preterm | 290 | 9.2 | 2.30 (2.03 to 2.59) | 2.18 (1.93 to 2.46) | <.001 | 5.2 (4.1 to 6.2) | 55.9 | 6.0 |
| Early term | 829 | 5.8 | 1.45 (1.34 to 1.57) | 1.40 (1.29 to 1.51) | <.001 | 1.7 (1.3 to 2.1) | 29.2 | 7.5 |
| Full term | 2395 | 4.1 | 1 [Reference] | 1 [Reference] | NA | 0 [Reference] | NA | NA |
| Postterm | 375 | 4.8 | 1.10 (0.99 to 1.23) | 1.13 (1.02 to 1.26) | .03 | 0.7 (0.2 to 1.2) | 14.9 | 2.0 |
| Per additional week (trend) | NA | NA | 0.86 (0.85 to 0.87) | 0.87 (0.86 to 0.88) | <.001 | NA | NA | NA |
| Attained ages <1 y | ||||||||
| Preterm | 233 | 119.6 | 4.69 (4.04 to 5.43) | 4.49 (3.86 to 5.22) | <.001 | 94.1 (78.7 to 109.6) | 78.7 | 19.4 |
| Extremely preterm | 31 | 601.6 | 22.91 (15.99 to 32.83) | 21.03 (14.64 to 30.20) | <.001 | 576.2 (364.4 to 787.9) | 95.8 | 4.0 |
| Moderately preterm | 65 | 164.1 | 6.42 (4.98 to 8.27) | 6.08 (4.70 to 7.86) | <.001 | 138.7 (98.7 to 178.6) | 84.5 | 7.1 |
| Late preterm | 137 | 91.3 | 3.58 (2.98 to 4.30) | 3.47 (2.88 to 4.17) | <.001 | 65.8 (50.4 to 81.2) | 72.1 | 11.6 |
| Early term | 334 | 46.8 | 1.84 (1.61 to 2.09) | 1.76 (1.54 to 2.00) | <.001 | 21.3 (16.0 to 26.7) | 45.6 | 14.5 |
| Full term | 713 | 25.4 | 1 [Reference] | 1 [Reference] | NA | 0 [Reference] | NA | NA |
| Postterm | 91 | 27.2 | 1.07 (0.86 to 1.33) | 1.11 (0.89 to 1.38) | .35 | 1.7 (−4.2 to 7.6) | 6.3 | 0.7 |
| Per additional week (trend) | NA | NA | 0.81 (0.80 to 0.82) | 0.82 (0.80 to 0.83) | <.001 | NA | NA | NA |
| Attained ages 1-17 y | ||||||||
| Preterm | 99 | 3.9 | 3.41 (2.74 to 4.25) | 3.42 (2.75 to 4.27) | <.001 | 2.8 (2.0 to 3.5) | 70.7 | 13.5 |
| Extremely preterm | 8 | 14.2 | 12.09 (6.00 to 24.33) | 12.81 (6.35 to 25.83) | <.001 | 13.1 (3.2 to 22.9) | 92.0 | 1.7 |
| Moderately preterm | 26 | 5.1 | 4.48 (3.01 to 6.66) | 4.59 (3.08 to 6.84) | <.001 | 4.0 (2.0 to 6.0) | 77.7 | 4.5 |
| Late preterm | 65 | 3.3 | 2.88 (2.22 to 3.74) | 2.88 (2.21 to 3.74) | <.001 | 2.2 (1.3 to 3.0) | 65.3 | 8.7 |
| Early term | 171 | 1.8 | 1.61 (1.35 to 1.93) | 1.60 (1.34 to 1.91) | <.001 | 0.7 (0.4 to 1.0) | 38.2 | 11.0 |
| Full term | 421 | 1.1 | 1 [Reference] | 1 [Reference] | NA | 0 [Reference] | NA | NA |
| Postterm | 46 | 1.0 | 0.88 (0.65 to 1.20) | 0.87 (0.64 to 1.18) | .36 | −0.1 (−0.5 to 0.2) | 12.5g | 1.4h |
| Per additional week (trend) | NA | NA | 0.84 (0.81 to 0.86) | 0.83 (0.81 to 0.86) | <.001 | NA | NA | NA |
| Attained ages 18-43 y | ||||||||
| Preterm | 128 | 10.0 | 1.56 (1.30 to 1.87) | 1.42 (1.19 to 1.71) | <.001 | 3.4 (1.6 to 5.2) | 34.2 | 3.1 |
| Extremely preterm | 6 | 31.7 | 5.40 (2.42 to 12.05) | 4.72 (2.11 to 10.52) | <.001 | 25.2 (−0.2 to 50.6) | 79.3 | 0.4 |
| Moderately preterm | 34 | 13.8 | 2.16 (1.54 to 3.04) | 1.93 (1.37 to 2.71) | <.001 | 7.2 (2.6 to 11.8) | 52.3 | 1.4 |
| Late preterm | 88 | 8.7 | 1.35 (1.09 to 1.67) | 1.24 (1.00 to 1.54) | .05 | 2.1 (0.2 to 3.9) | 24.1 | 1.6 |
| Early term | 324 | 7.3 | 1.16 (1.02 to 1.31) | 1.09 (0.97 to 1.24) | .15 | 0.7 (−0.2 to 1.6) | 9.6 | 2.0 |
| Full term | 1261 | 6.6 | 1 [Reference] | 1 [Reference] | NA | 0 [Reference] | NA | NA |
| Postterm | 238 | 8.2 | 1.15 (1.00 to 1.33) | 1.19 (1.04 to 1.37) | .01 | 1.6 (0.5 to 2.7) | 19.9 | 3.2 |
| Per additional week (trend) | NA | NA | 0.95 (0.93 to 0.98) | 0.97 (0.95 to 0.99) | .01 | NA | NA | NA |
Abbreviations: AFe, attributable fraction in the exposed; NA, not applicable; PAF, population-attributable fraction.
Preterm birth was defined as any at a gestational age less than 37 weeks; extremely preterm, at 22 to 27 weeks’ gestational age; moderately preterm, at 28 to 33 weeks’ gestational age; late preterm, at 34 to 36 weeks’ gestational age; early term, at 37 to 38 weeks’ gestational age; full term, at 39 to 41 weeks’ gestational age; and postterm, at 42 weeks’ gestational age or more.
Incidence rate per 100 000 person-years.
Adjusted for child characteristics (birth year, sex, birth order, and family history of heart failure or ischemic heart disease) and maternal characteristics (age, education, birth country, body mass index, smoking, preeclampsia, other hypertensive disorders, and diabetes).
Incidence rate difference per 100 000 person-years.
Attributable fraction among the exposed.
Population-attributable fraction.
Prevented fraction among the exposed.
Population-prevented fraction.