Table 2. Associations Between Preterm Birth and Annual Income at or After the Age of 18 Years for Individuals Born in Canada, 1990-1996, in Comparison With Term-Born Childrena.
| Category | Overall | Family quintile 1 (lowest) | Family quintile 2 | Family quintile 3 | Family quintile 4 | Family quintile 5 (highest) |
|---|---|---|---|---|---|---|
| Unmatched cohort, mean annual employment income difference, CAD$ (95% CI) b | ||||||
| Preterm (<37 wk) | −1579 (−1663 to −1495) | −1559 (−1710 to −1409) | −1838 (−2005 to −1670) | −1406 (−1591 to −1220) | −1006 (−1201 to −812) | −841 (−1074 to −608) |
| Gestational age category, wk | ||||||
| 34-36 | −1349 (−1443 to −1255) | −1405 (−1575 to −1235) | −1631 (−1817 to −1445) | −1187 (−1393 to −980) | −784 (−1001 to −568) | −490 (−749 to −232) |
| 32-33 | −1670 (−1921 to −1419) | −1605 (−2043 to −1167) | −1818 (−2325 to −1311) | −1820 (−2371 to −1269) | −955 (−1530 to −380) | −1016 (−1732 to −300) |
| 28-31 | −2687 (−2967 to −2408) | −2206 (−2690 to −1722) | −2912 (−3493 to −2331) | −1981 (−2610 to −1352) | −1989 (−2667 to −1311) | −3109 (−3859 to −2360) |
| 24-27 | −5427 (−5859 to −4996) | −4336 (−5078 to −3593) | −5221 (−6030 to −4413) | −5478 (−6429 to −4528) | −5521 (−6563 to −4480) | −5308 (−6647 to −3970) |
| Matched cohort model 1: mean annual employment income difference, CAD$ (95% CI) c | ||||||
| Preterm (<37 wk) | −697 (−801 to −592) | −814 (−1011 to −618) | −786 (−993 to −579) | −786 (−1011 to −560) | −538 (−773 to −303) | −545 (−830 to −259) |
| Gestational age category, wk | ||||||
| 34-36 | −459 (−573 to −345) | −621 (−840 to −402) | −569 (−796 to −341) | −527 (−773 to −280) | −302 (−559 to −45) | −253 (−559 to 54) |
| 32-33 | −902 (−1231 to −573) | −952 (−1557 to −347) | −853 (−1528 to −178) | −1157 (−1865 to −448) | −694 (−1408 to 19) | −898 (−1840 to 44) |
| 28-31 | −2001 (−2362 to −1640) | −1717 (−2364 to −1071) | −2165 (−2911 to −1419) | −1951 (−2754 to −1149) | −1582 (−2475 to −688) | −2658 (−3585 to −1730) |
| 24-27 | −4481 (−5055 to −3908) | −3902 (−4947 to −2858) | −3979 (−5014 to −2944) | −5177 (−6501 to −3854) | −5312 (−6554 to −4069) | −3954 (−5787 to −2121) |
| Matched cohort model 2: mean annual employment income difference, CAD$ (95% CI) c , d | ||||||
| Preterm (<37 wk) | −687 (−788 to −586) | −807 (−998 to −617) | −775 (−975 to −576) | −776 (−993 to −559) | −531 (−758 to −305) | −528 (−806 to −249) |
| Gestational age category, wk | ||||||
| 34-36 | −455 (−566 to −345) | −617 (−829 to −405) | −565 (−784 to −346) | −526 (−763 to −289) | −300 (−547 to −52) | −246 (−544 to 53) |
| 32-33 | −887 (−1208 to −565) | −948 (−1540 to −356) | −825 (−1482 to −168) | −1145 (−1821 to −469) | −684 (−1373 to 5) | −875 (−1802 to 52) |
| 28-31 | −1950 (−2303 to −1597) | −1716 (−2345 to −1086) | −2121 (−2848 to −1394) | −1865 (−2644 to −1086) | −1491 (−2370 to −612) | −2590 (−3490 to −1689) |
| 24-27 | −4278 (−4835 to −3721) | −3775 (−4779 to −2771) | −3833 (−4846 to −2820) | −4864 (−6136 to −3591) | −5196 (−6415 to −3978) | −3525 (−5293 to −1758) |
| Unmatched cohort, ratio of income per year (95% CI) b | ||||||
| Preterm (<37 wk) | 0.92 (0.92 to 0.93) | 0.91 (0.90 to 0.92) | 0.91 (0.90 to 0.92) | 0.93 (0.92 to 0.94) | 0.95 (0.94 to 0.96) | 0.96 (0.95 to 0.97) |
| Gestational age category, wk | ||||||
| 34-36 | 0.93 (0.93 to 0.94) | 0.92 (0.91 to 0.93) | 0.92 (0.91 to 0.93) | 0.94 (0.93 to 0.95) | 0.96 (0.95 to 0.97) | 0.98 (0.97 to 0.99) |
| 32-33 | 0.92 (0.91 to 0.93) | 0.91 (0.88 to 0.93) | 0.91 (0.88 to 0.93) | 0.91 (0.89 to 0.94) | 0.96 (0.93 to 0.98) | 0.96 (0.93 to 0.99) |
| 28-31 | 0.87 (0.86 to 0.88) | 0.87 (0.85 to 0.90) | 0.85 (0.83 to 0.88) | 0.91 (0.88 to 0.94) | 0.91 (0.88 to 0.94) | 0.87 (0.83 to 0.90) |
| 24-27 | 0.74 (0.72 to 0.76) | 0.75 (0.71 to 0.79) | 0.74 (0.70 to 0.78) | 0.74 (0.70 to 0.79) | 0.74 (0.70 to 0.79) | 0.77 (0.71 to 0.83) |
| Matched cohort model 1: ratio of income per year (95% CI) c | ||||||
| Preterm (<37 wk) | 0.96 (0.96 to 0.97) | 0.95 (0.94 to 0.96) | 0.96 (0.95 to 0.97) | 0.96 (0.95 to 0.97) | 0.97 (0.96 to 0.99) | 0.98 (0.96 to 0.99) |
| Gestational age category, wk | ||||||
| 34-36 | 0.98 (0.97 to 0.98) | 0.96 (0.95 to 0.98) | 0.97 (0.96 to 0.98) | 0.97 (0.96 to 0.99) | 0.99 (0.97 to 1.00) | 0.99 (0.98 to 1.00) |
| 32-33 | 0.96 (0.94 to 0.97) | 0.94 (0.91 to 0.98) | 0.96 (0.92 to 0.99) | 0.94 (0.91 to 0.98) | 0.97 (0.93 to 1.00) | 0.96 (0.92 to 1.00) |
| 28-31 | 0.90 (0.88 to 0.92) | 0.90 (0.86 to 0.94) | 0.89 (0.85 to 0.93) | 0.91 (0.87 to 0.95) | 0.93 (0.89 to 0.97) | 0.88 (0.84 to 0.92) |
| 24-27 | 0.77 (0.75 to 0.80) | 0.77 (0.72 to 0.83) | 0.79 (0.74 to 0.84) | 0.75 (0.70 to 0.82) | 0.75 (0.69 to 0.80) | 0.82 (0.75 to 0.91) |
| Matched cohort model 2: ratio of income per year (95% CI) c , d | ||||||
| Preterm (<37 wk) | 0.97 (0.96 to 0.97) | 0.95 (0.94 to 0.97) | 0.96 (0.94 to 0.97) | 0.96 (0.95 to 0.98) | 0.97 (0.96 to 0.99) | 0.99 (0.97 to 1.00) |
| Gestational age category, wk | ||||||
| 34-36 | 0.98 (0.97 to 0.98) | 0.96 (0.95 to 0.98) | 0.97 (0.95 to 0.98) | 0.97 (0.96 to 0.99) | 0.98 (0.97 to 1.00) | 1.00 (0.98 to 1.01) |
| 32-33 | 0.96 (0.94 to 0.98) | 0.95 (0.91 to 0.99) | 0.94 (0.90 to 0.98) | 0.96 (0.91 to 1.00) | 0.97 (0.93 to 1.01) | 0.97 (0.93 to 1.03) |
| 28-31 | 0.90 (0.88 to 0.92) | 0.91 (0.86 to 0.96) | 0.88 (0.84 to 0.92) | 0.90 (0.86 to 0.95) | 0.90 (0.86 to 0.95) | 0.89 (0.84 to 0.94) |
| 24-27 | 0.80 (0.77 to 0.84) | 0.80 (0.73 to 0.87) | 0.79 (0.72 to 0.86) | 0.81 (0.73 to 0.89) | 0.76 (0.69 to 0.83) | 0.89 (0.80 to 0.99) |
a
Current exhange rate: $1 = CAD $1.37.
b
For 1 614 150 individuals; 11 727 110 person-years.
c
For 968 550 individuals with gestational age less than 37 weeks (6 966 590 person-years); for 897 970 individuals with gestational age 34 to 36 weeks (6 465 520 person-years); for 315 050 individuals with gestational age 32 to 33 weeks (2 207 450 person-years); for 229 770 individuals with gestational age 28 to 31 weeks (1 611 600 person-years); for 103 160 individuals with gestational age 24 to 27 weeks (712 350 person-years).
d
Model 2 used the matched sample and further adjusted for the calendar year and age modeled using restricted cubic splines.