Table 1.
Description of the study population and green space exposure levels by maternal characteristics.
| Characteristics | Preterm birth (< 37 weeks) n = 341,123 | Term birth (≥ 37 weeks) n = 3,412,676 | Total births n = 3,753,799 | NDVI 250m mean (SD) |
|---|---|---|---|---|
| Maternal age, years, n (%) | ||||
| <15 | 759 (0.002) | 3857 (0.001) | 4616 (0.001) | 0.33 (0.10) |
| 15 to 19 | 38116 (11.2) | 311818 (9.1) | 349934 (9.3) | 0.34 (0.10) |
| 20 to 24 | 77511 (22.7) | 778706 (22.8) | 856217 (22.8) | 0.34 (0.10) |
| 25 to 29 | 82171 (24.1) | 908515 (26.6) | 990686 (26.4) | 0.35 (0.10) |
| 30 to 34 | 78026 (22.9) | 840404 (24.6) | 918430 (24.5) | 0.36 (0.11) |
| 35 to 39 | 49611 (14.5) | 459108 (13.5) | 508769 (13.6) | 0.37 (0.11) |
| 40 to 44 | 13904 (4.1) | 104481 (3.1) | 118385 (3.2) | 0.38 (0.12) |
| ≥ 45 | 961 (0.003) | 5362 (0.002) | 6259 (0.002) | 0.38 (0.12) |
| Maternal race/ethnicity, n (%) | ||||
| African American | 26111 (7.8) | 169693 (5.0) | 195804 (5.3) | 0.33 (0.09) |
| Asian | 37326 (11.1) | 397742 (11.8) | 435068 (11.7) | 0.36 (0.10) |
| Hispanic | 185293 (55.0) | 1746125 (51.8) | 1931418 (52.1) | 0.33 (0.09) |
| Non-Hispanic white | 79999 (23.7) | 982680 (29.1) | 1062679 (29.0) | 0.40 (0.12) |
| Multiple/other | 8365 (2.5) | 76790 (2.3) | 85155 (2.3) | 0.37 (0.12) |
| Maternal education, n (%) | ||||
| ≤ 8th grade | 39709 (12.0) | 350658 (10.5) | 390367 (10.7) | 0.33 (0.10) |
| 9th grade – high school | 164595 (49.6) | 1492342 (44.8) | 1656937 (45.3) | 0.34 (0.10) |
| College (< 4 years) | 66386 (20.0) | 678255 (20.4) | 744641 (20.3) | 0.36 (0.11) |
| College (≥ 4 years) | 61311 (18.5) | 806717 (24.2) | 868028 (23.7) | 0.39 (0.11) |
| Median annual income by census block group, n (%) | ||||
| ≤ $31,033 | 98646 (29.0) | 836881 (24.6) | 935527 (25.0) | 0.31 (0.10) |
| $31,034–$42,534 | 87820 (25.8) | 847690 (24.9) | 935510 (25.0) | 0.34 (0.10) |
| $42,535–$60,221 | 82012 (24.1) | 853496 (25.1) | 935508 (25.0) | 0.36 (0.10) |
| ≥ $60,222 | 71664 (21.1) | 863678 (25.4) | 935342 (25.0) | 0.40 (0.10) |
| Season of conception, n (%) | ||||
| Warm season | 166990 (49.0) | 1652314 (48.4) | 1819304 (48.5) | 0.35 (0.11) |
| Cool season | 174133 (51.0) | 1760362 (51.6) | 1934495 (51.5) | 0.35 (0.11) |
| Rural/urban status, n (%) | ||||
| Rural | 30612 (9.0) | 317371 (9.3) | 347983 (9.3) | 0.45 (0.16) |
| Urban | 310084 (91.0) | 3089453 (90.7) | 3399537 (90.7) | 0.35 (0.09) |
SD, standard deviation.