Table 1 Summary of sociodemographic and clinical characteristics of the study population
From: Toxic metal mixtures in private well water and increased risk for preterm birth in North Carolina
|  | All births | Term birth ≥ 37 weeks’ gestation | Preterm birth < 37 weeks’ gestation |
|---|---|---|---|
N (%) | N (%) | N (%) | |
1,329,071 | 1,368,968 | 124,227 | |
Fetal sex | |||
 Male | 675,994 (50.9) | 617,728 (50.7) | 58,266 (53.0) |
 Female | 653,074 (49.1) | 601,443 (49.3) | 51,631 (47.0) |
 Missing | 3 | 1 | 2 |
Race/ethnicity (of birthing parent) | |||
 White non-Hispanic | 773,537 (58.2) | 715,722 (58.7) | 57,815 (52.6) |
 Black non-Hispanic | 292,088 (22.0) | 258,455 (21.2) | 33,633 (30.6) |
 Hispanic | 200,411 (15.1) | 186,729 (15.3) | 13,682 (12.4) |
 Asian/Pacific Islander | 41,364 (3.1) | 38,595 (3.2) | 2769 (2.5) |
 American Indian | 19,286 (1.5) | 17,484 (1.4) | 1802 (1.6) |
 Other/unknown | 2385 (0.2) | 2187 (0.2) | 198 (0.2) |
Age | |||
 < 20 | 134,939 (10.2) | 122,173 (10.0) | 12,766 (11.6) |
 < 30, >  = 20 | 711,355 (53.5) | 654,089 (53.7) | 57,266 (52.1) |
 < 40, >  = 30 | 453,069 (34.1) | 416,445 (34.2) | 36,624 (33.3) |
 >  = 40 | 29,690 (2.2) | 26,451 (2.2) | 3239 (2.9) |
 Missing | 23 | 19 | 4 |
Education | |||
 Less than high school | 249,935 (20.4) | 226,962 (20.2) | 22,973 (22.7) |
 Completed high school | 319,452 (26.1) | 290,188 (25.9) | 29,264 (28.9) |
 More than high school | 654,490 (53.5) | 605,434 (53.9) | 49,056 (48.4) |
 Missing | 118,089 | 108,399 | 9690 |
Smoking during pregnancy | |||
 Non-smoker | 1,086,801 (88.9) | 1,001,059 (89.2) | 85,742 (84.8) |
 Smoker | 136,343 (11.1) | 120,916 (10.8) | 15,427 (15.2) |
 Missing | 118,824 | 109,012 | 9812 |
Season of conception | |||
 Winter (Dec, Jan, Feb) | 336,098 (25.3) | 308,664 (25.3) | 27,434 (25.0) |
 Spring (Mar, Apr, May) | 329,472 (24.8) | 301,626 (24.7) | 27,846 (25.3) |
 Summer (June, Jul, Aug) | 324,489 (24.4) | 297,646 (24.4) | 26,843 (24.4) |
 Fall (Sept, Oct, Nov) | 339,012 (25.5) | 311,236 (25.5) | 27,776 (25.3) |
Delivery | |||
 Vaginal | 947,615 (71.3) | 878,675 (72.1) | 68,940 (62.7) |
 Caesarean | 381,239 (28.7) | 340,309 (27.9) | 40,930 (37.3) |
 Missing | 250 | 214 | 36 |
Preterm birth severity subtypes | |||
 Extreme preterm birth (< 28 weeks) | 7718 (0.6) | n/a | 7718 (7.0) |
 Very preterm birth (28 to < 32 weeks) | 9495 (0.7) | n/a | 9495 (8.6) |
 Moderate to late preterm birth (32 to < 37 weeks) | 92,686 (7.0) | n/a | 92,686 (84.3) |