Table 1.
Characteristic of study population by early delivery status (n = 223,375).
| Characteristics | Early preterm birth (< 34 weeks) (n = 8,767) | Late preterm birth (34–36 weeks) (n = 17,363) | Early term birth (37–38 weeks) (n = 66,580) | Full-term birth (≥ 39 weeks) (n = 130,665) | |||
|---|---|---|---|---|---|---|---|
| n (%) | p-Valuea | n (%) | p-Valuea | n (%) | p-Valuea | n (%) | |
| Race/ethnicity | < 0.0001 | < 0.0001 | < 0.0001 | ||||
| Non-Hispanic white | 2,944 (33.6) | 7,640 (44.0) | 32,525 (48.9) | 67,432 (51.6) | |||
| Non-Hispanic black | 3,332 (38.0) | 5,128 (29.5) | 15,440 (23.2) | 26,355 (20.2) | |||
| Hispanic | 1,551 (17.7) | 3,023 (17.4) | 11,445 (17.2) | 22,792 (17.4) | |||
| Asian/Pacific Islander | 200 (2.3) | 571 (3.3) | 3,079 (4.6) | 5,325 (4.1) | |||
| Other | 311 (3.6) | 414 (2.4) | 1,507 (2.3) | 2,998 (2.3) | |||
| Unknown | 429 (4.9) | 587 (3.4) | 2,584 (3.9) | 5,763 (4.4) | |||
| Maternal age (years) | 0.4449 | 0.8628 | < 0.0001 | ||||
| < 20 | 1,124 (12.8) | 1,895 (10.9) | 5,669 (8.5) | 12,007 (9.2) | |||
| 20–24 | 2,243 (25.6) | 4,398 (25.3) | 16,047 (24.1) | 33,893 (25.9) | |||
| 25–29 | 1,992 (22.7) | 4,536 (26.1) | 18,614 (28.0) | 37,070 (28.4) | |||
| 30–34 | 1,831 (20.9) | 3,714 (21.4) | 15,519 (23.3) | 29,081 (22.3) | |||
| ≥ 35 | 1,556 (17.8) | 2,804 (16.2) | 10,638 (16.0) | 18,437 (14.1) | |||
| Unknown | 21 (0.2) | 16 (0.1) | 93 (0.1) | 177 (0.1) | |||
| Infant sex | < 0.0001 | < 0.0001 | < 0.0001 | ||||
| Female | 4,083 (46.6) | 8,152 (47.0) | 32,050 (48.1) | 64,643 (49.5) | |||
| Male | 4,524 (51.6) | 9,138 (52.6) | 34,397 (51.7) | 65,873 (50.4) | |||
| Unknown | 160 (1.8) | 73 (0.4) | 133 (0.2) | 149 (0.1) | |||
| Marital status | < 0.0001 | < 0.0001 | 0.1187 | ||||
| Not married | 4,562 (52.0) | 7,854 (45.2) | 24,746 (37.2) | 47,832 (36.6) | |||
| Married | 3,802 (43.4) | 8,927 (51.4) | 39,615 (59.5) | 78,831 (60.3) | |||
| Unknown | 403 (4.6) | 582 (3.4) | 2,219 (3.3) | 4,002 (3.1) | |||
| Parity | 0.6779 | < 0.0001 | < 0.0001 | ||||
| 0 | 3,852 (43.9) | 6,641 (38.3) | 23,311 (35.0) | 55,220 (42.3) | |||
| 1 | 2,253 (25.7) | 4,933 (28.4) | 22,130 (33.2) | 39,073 (29.9) | |||
| ≥ 2 | 2,662 (30.4) | 5,789 (33.3) | 21,139 (31.8) | 36,372 (27.8) | |||
| Prepregnancy BMI | < 0.0001 | < 0.0001 | < 0.0001 | ||||
| < 18.5 | 282 (3.2) | 702 (4.0) | 2,597 (3.9) | 4,395 (3.4) | |||
| 18.5–24.9 | 2,195 (25.0) | 5,577 (32.1) | 23,087 (34.7) | 48,182 (36.9) | |||
| 25–29.9 | 1,156 (13.2) | 2,528 (14.6) | 9,826 (14.8) | 19,985 (15.3) | |||
| ≥ 30 | 1,235 (14.1) | 2,431 (14.0) | 8,590 (12.9) | 15,619 (12.0) | |||
| Unknown | 3,899 (44.5) | 6,125 (35.3) | 22,480 (33.8) | 42,484 (32.5) | |||
| Smoking during pregnancy | 1,002 (11.4) | < 0.0001 | 1,665 (9.6) | < 0.0001 | 4,454 (6.7) | < 0.0001 | 7,809 (6.0) |
| Alcohol use during pregnancy | 284 (3.2) | < 0.0001 | 384 (2.2) | < 0.0001 | 1,222 (1.8) | 0.0155 | 2,200 (1.7) |
| Hypertensive disorders of pregnancy | 1,675 (19.1) | < 0.0001 | 2,501 (14.4) | < 0.0001 | 4,551 (6.8) | < 0.0001 | 4,317 (3.3) |
| Gestational diabetes | 533 (6.1) | < 0.0001 | 1,325 (7.6) | < 0.0001 | 4,548 (6.8) | < 0.0001 | 4,934 (3.8) |
| Insurance type | < 0.0001 | < 0.0001 | 0.3368 | ||||
| Private | 3,863 (44.1) | 8,592 (49.5) | 37,760 (56.7) | 74,688 (57.2) | |||
| Public | 3,930 (44.8) | 6,760 (38.9) | 21,563 (32.4) | 39,894 (30.5) | |||
| Other | 166 (1.9) | 294 (9.9) | 875 (1.3) | 1,647 (1.3) | |||
| Unknown | 808 (9.2) | 1,717 (9.9) | 6,382 (9.6) | 14,436 (11.1) | |||
| Month of conception | < 0.0001 | 0.0016 | 0.5574 | ||||
| January | 770 (8.8) | 1,488 (8.6) | 4,953 (7.4) | 8,956 (6.9) | |||
| February | 678 (7.7) | 1,119 (6.4) | 4,182 (6.3) | 8,185 (6.3) | |||
| March | 713 (8.1) | 1,218 (7.0) | 4,782 (7.2) | 9,349 (7.2) | |||
| April | 634 (7.2) | 1,277 (7.4) | 5,090 (7.6) | 10,573 (8.1) | |||
| May | 668 (7.6) | 1,431 (8.2) | 5,823 (8.8) | 11,310 (8.7) | |||
| June | 676 (7.7) | 1,472 (8.5) | 5,503 (8.3) | 11,019 (8.4) | |||
| July | 764 (8.7) | 1,577 (9.1) | 5,634 (8.5) | 11,302 (8.7) | |||
| August | 726 (8.3) | 1,502 (8.7) | 5,969 (9.0) | 11,520 (8.8) | |||
| September | 677 (7.7) | 1,482 (8.5) | 5,767 (8.7) | 11,524 (8.8) | |||
| October | 807 (9.2) | 1,513 (8.7) | 6,131 (9.2) | 12,425 (9.5) | |||
| November | 819 (9.3) | 1,576 (9.1) | 6,209 (9.3) | 12,329 (9.4) | |||
| December | 835 (9.5) | 1,708 (9.8) | 6,537 (9.8) | 12,173 (9.3) | |||
| ap-Values were obtained by generalized estimating equations, accounting for multiple pregnancies of the same woman during the study period. | |||||||