TABLE 1.
Characteristics of VLBW Infants in the NRN Cohort Born in 1998–2007
| Characteristica | All infants, N = 37 262 | Infants With BDs, N = 1776 | Infants Without BDs, N = 35 486 | P b |
|---|---|---|---|---|
| Maternal age, y | ||||
| Mean (SD) | 27.0 (6.7) | 28.0 (7.1) | 27.0 (6.7) | .007 |
| Category, n (%) | ||||
| <25 | 14 869 (40) | 685 (39) | 14 184 (40) | — |
| 25–29 | 8677 (23) | 407 (23) | 8270 (23) | — |
| 30–34 | 7887 (21) | 326 (18) | 7561 (21) | — |
| 35–39 | 4546 (12) | 259 (15) | 4287 (12) | — |
| 40+ | 1263 (3) | 99 (6) | 1164 (3) | — |
| Antenatal steroids, n (%) | 27 501 (74) | 1093 (62) | 26 408 (75) | <.001 |
| Cesarean delivery, n (%) | 22 337 (60) | 1122 (63) | 21 215 (60) | .005 |
| Multiple birth, n (%) | 9573 (26) | 328 (18) | 9245 (26) | <.001 |
| GA, wk | ||||
| Mean (SD) | 28 (3.1) | 29 (3.5) | 28 (3.0) | <.001 |
| Category, n (%) | ||||
| <22 | 377 (1) | 20 (1) | 357 (1) | — |
| 22–24 | 6051 (16) | 148 (8) | 5903 (17) | — |
| 25–28 | 15 531 (42) | 583 (33) | 14 948 (42) | — |
| 29–32 | 13 158 (35) | 740 (42) | 12 418 (35) | — |
| 33+ | 2135 (6) | 284 (16) | 1851 (5) | — |
| SGA, n (%) | 7731 (21) | 702 (40) | 7029 (20) | <.001 |
| SGA by GA category, % | <.001 | |||
| <22 | 0 | 0 | 0 | — |
| 22–24 | 4 | 4 | 4 | — |
| 25–28 | 8 | 14 | 8 | — |
| 29–32 | 31 | 45 | 30 | — |
| 33+ | 100 | 100 | 100 | — |
| BW, g | ||||
| Mean (SD) | 1007 (304) | 1057 (294) | 1004 (305) | <.001 |
| Category, n (%) | ||||
| 401–750 | 9526 (26) | 325 (18) | 9201 (26) | — |
| 751–1000 | 8546 (23) | 422 (24) | 8124 (23) | — |
| 1001–1250 | 8985 (24) | 467 (26) | 8518 (24) | — |
| 1251–1500 | 10 205 (27) | 562 (32) | 9643 (27) | — |
| Boy, n (%) | 18 934 (51) | 842 (47) | 18 092 (51) | .004 |
| Race/ethnicity, n (%) | <.001 | |||
| Non-Hispanic black | 14 249 (38) | 534 (30) | 13 715 (39) | — |
| Non-Hispanic white | 14 962 (40) | 787 (45) | 14 175 (40) | — |
| Hispanic | 6317 (17) | 367 (21) | 5950 (17) | — |
| Other | 1630 (4) | 77 (4) | 1553 (4) | — |
| Outborn, n (%) | 4315 (12) | 336 (19) | 3979 (11) | <.001 |
| Apgar ≤ 3 at 1 min, n (%) | 11 748 (32) | 791 (45) | 10 957 (31) | <.001 |
| Apgar ≤ 3 at 5 min, n (%) | 4230 (12) | 369 (21) | 3861 (11) | <.001 |
Information was missing for maternal age: 20 infants; antenatal steroids: 181; cesarean delivery: 29; multiple birth: 1; GA: 10; SGA: 10; gender: 4; race: 104; Apgar at 1 minute: 519; Apgar at 5 minutes: 504.
P value for a test between infants with BDs versus no BDs by the Wilcoxon test (means for maternal age, BW, GA), Fisher’s exact test, or the Cochran-Mantel-Haenszel χ2 test (SGA controlling for GA). Tests assessed differences in the distribution of each characteristic overall. P values for differences in the categorical distributions of maternal age, BW, and GA are not shown, and tests between individual categories (eg, Non-Hispanic black) of characteristics categorized as more than two levels were not performed (as indicated by dashes).