Table 2.
Associations between gestational age at birth (1973–2013) and risk of ASD (1987–2015), Sweden.
| Cases | Prev.a | Unadjusted | Adjustedb |
Unadjusted | AFec | PAFd | ||
|---|---|---|---|---|---|---|---|---|
| (n) | (%) | PR (95% CI) | PR (95% CI) | P | PD (95% CI) | (%) | (%) | |
| Total cohort | ||||||||
| Preterm (<37 wks) | 4,147 | 2.1 | 1.57 (1.52, 1.62) | 1.40 (1.36, 1.45) | <0.001 | 0.7 (0.7, 0.8) | 37.7 | 3.7 |
| Extremely preterm (22–27 wks) | 311 | 6.1 | 4.54 (4.08, 5.06) | 3.87 (3.48, 4.31) | <0.001 | 4.7 (4.1, 5.5) | 83.7 | 0.7 |
| Very to moderate preterm (28–33 wks) | 1,023 | 2.6 | 1.91 (1.80, 2.03) | 1.65 (1.55, 1.76) | <0.001 | 1.2 (1.1, 1.4) | 50.2 | 1.3 |
| Late preterm (34–36 wks) | 2,813 | 1.9 | 1.38 (1.33, 1.44) | 1.25 (1.20, 1.30) | <0.001 | 0.5 (0.5, 0.6) | 28.1 | 1.9 |
| Early term (37–38 wks) | 11,451 | 1.6 | 1.19 (1.16, 1.21) | 1.12 (1.10, 1.14) | <0.001 | 0.2 (0.2, 0.3) | 18.9 | 4.4 |
| Full-term (39–41 wks) | 37,940 | 1.4 | Reference | Reference | Reference | |||
| Post-term (≥42 wks) | 4,866 | 1.5 | 1.07 (1.04, 1.10) | 1.08 (1.05, 1.11) | <0.001 | 0.1 (0.0, 0.1) | 4.0 | 0.5 |
| Per additional week (trend) | 0.94 (0.93, 0.94) | 0.95 (0.95, 0.96) | <0.001 | |||||
|
| ||||||||
| Males | ||||||||
| Preterm (<37 wks) | 2,829 | 2.7 | 1.48 (1.42, 1.54) | 1.35 (1.30, 1.40) | <0.001 | 0.9 (0.8, 1.0) | 33.3 | 3.3 |
| Extremely preterm 22–27 wks) | 214 | 8.1 | 4.49 (3.94, 5.10) | 3.72 (3.27, 4.23) | <0.001 | 6.3 (5.2, 7.3) | 83.6 | 0.7 |
| Very to moderate preterm (28–33 wks) | 687 | 3.1 | 1.74 (1.61, 1.87) | 1.54 (1.43, 1.66) | <0.001 | 1.3 (1.1, 1.6) | 45.3 | 1.2 |
| Late preterm (34–36 wks) | 1,928 | 2.4 | 1.31 (1.25, 1.37) | 1.21 (1.16, 1.27) | <0.001 | 0.6 (0.5, 0.7) | 23.5 | 1.6 |
| Early term (37–38 wks) | 7,683 | 2.1 | 1.16 (1.13, 1.19) | 1.11 (1.08, 1.13) | <0.001 | 0.3 (0.2, 0.3) | 16.1 | 3.7 |
| Full-term (39–41 wks) | 25,648 | 1.8 | Reference | Reference | Reference | |||
| Post-term (≥42 wks) | 3,397 | 1.9 | 1.03 (1.00, 1.07) | 1.06 (1.02, 1.09) | 0.002 | 0.1 (0.0, 0.1) | 4.5 | 0.5 |
| Per additional week (trend) | 0.94 (0.94, 0.95) | 0.96 (0.95, 0.96) | <0.001 | |||||
|
| ||||||||
| Females | ||||||||
| Preterm (<37 wks) | 1,318 | 1.5 | 1.67 (1.58, 1.77) | 1.53 (1.45, 1.62) | <0.001 | 0.6 (0.5, 0.7) | 41.7 | 4.0 |
| Extremely preterm (22–27 wks) | 97 | 4.0 | 4.52 (3.71, 5.49) | 4.19 (3.45, 5.09) | <0.001 | 3.1 (2.3, 3.9) | 83.4 | 0.7 |
| Very to moderate preterm (28–33 wks) | 336 | 1.9 | 2.14 (1.92, 2.38) | 1.92 (1.72, 2.14) | <0.001 | 1.0 (0.8, 1.2) | 55.5 | 1.5 |
| Late preterm (34–36 wks) | 885 | 1.3 | 1.45 (1.35, 1.55) | 1.34 (1.25, 1.43) | <0.001 | 0.4 (0.3, 0.5) | 32.0 | 2.1 |
| Early term (37–38 wks) | 3,768 | 1.1 | 1.22 (1.18, 1.27) | 1.16 (1.12, 1.20) | <0.001 | 0.2 (0.2, 0.2) | 22.4 | 5.3 |
| Full-term (39–41 wks) | 12,292 | 0.9 | Reference | Reference | Reference | |||
| Post-term (≥42 wks) | 1,469 | 1.0 | 1.07 (1.02, 1.13) | 1.12 (1.06, 1.18) | <0.001 | 0.1 (0.0, 0.1) | 7.0 | 0.8 |
| Per additional week (trend) | 0.93 (0.92, 0.93) | 0.94 (0.93, 0.95) | <0.001 | |||||
a
Cumulative prevalence.
b
Adjusted for birth year, sex, birth order, maternal factors (age, education, BMI, preeclampsia, other hypertensive disorders, diabetes), paternal factors (age, education), and family history of ASD.
c
Attributable fraction among the exposed.
d
Population attributable fraction.
PD = prevalence difference, PR = prevalence ratio