Table 1.
Maternal and infant characteristics for 34636 infants born at GA 22–28 weeks in NRN centers January 1, 1993 – December 31, 2012
| Total (N=34636) |
1993 (N=1433) |
2012 (N=1922) |
1993–1997 (N=7027) |
1998–2002 (N=9132) |
2003–2007 (N=9600) |
2008–2012 (N=8877) |
P-value for linear trend 1993–2012b | |
|---|---|---|---|---|---|---|---|---|
|
| ||||||||
| Maternal characteristicsa | ||||||||
|
| ||||||||
| Maternal age, y | ||||||||
| Mean (SD) | 27.0 (6.6) | 25.7 (6.5) | 27.8 (6.3) | 26.3 (6.7) | 26.8 (6.7) | 27.2 (6.6) | 27.5 (6.4) | <0.001 |
|
| ||||||||
| Race/ethnicity, No. (%) | <0.001 | |||||||
| Black, non-Hispanic | 14472 (42) | 781 (55) | 751 (39) | 3450 (49) | 3908 (43) | 3745 (39) | 3369 (38) | |
| White, non-Hispanic | 13124 (38) | 451 (31) | 796 (42) | 2483 (35) | 3491 (38) | 3557 (37) | 3593 (41) | |
| Hispanic | 5563 (16) | 174 (12) | 262 (14) | 903 (13) | 1425 (16) | 1825 (19) | 1410 (16) | |
| Other | 1377 (4) | 26 (2) | 101 (5) | 179 (3) | 280 (3) | 450 (5) | 468 (5) | |
|
| ||||||||
| ≥ 1 prenatal visit, No. (%) | 32235 (93) | 1233 (87) | 1835 (97) | 6296 (90) | 8498 (93) | 8997 (94) | 8444 (96) | <0.001 |
|
| ||||||||
| Insulin-dependent diabetes, No. (%) | 1317 (4) | 28 (2) | 96 (5) | 136 (2) | 302 (3) | 436 (5) | 443 (5) | <0.001 |
|
| ||||||||
| Hypertension, No. (%) | ||||||||
| All infants | 6991 (20) | 172 (12) | 508 (27) | 1067 (15) | 1607 (18) | 2121 (22) | 2196 (25) | <0.001 |
| By GA, w | ||||||||
| 22 | 94 (6) | 2 (3) | 6 (8) | 13 (4) | 19 (4) | 34 (8) | 28 (8) | |
| 23 | 242 (8) | 2 (2) | 25 (17) | 21 (3) | 49 (6) | 84 (10) | 88 (11) | |
| 24 | 596 (13) | 10 (6) | 49 (18) | 67 (8) | 122 (10) | 198 (14) | 209 (17) | |
| 25 | 1014 (19) | 23 (10) | 86 (28) | 139 (13) | 241 (17) | 304 (20) | 330 (24) | |
| 26 | 1289 (22) | 30 (12) | 93 (28) | 206 (17) | 297 (19) | 392 (25) | 394 (26) | |
| 27 | 1684 (25) | 49 (17) | 116 (33) | 282 (21) | 374 (22) | 498 (27) | 530 (31) | |
| 28 | 2072 (28) | 56 (18) | 133 (32) | 339 (22) | 505 (26) | 611 (30) | 617 (33) | |
|
| ||||||||
| Infant characteristics | ||||||||
|
| ||||||||
| Multiple birth, No. (%) | 8448 (24) | 265 (18) | 521 (27) | 1466 (21) | 2265 (25) | 2406 (25) | 2311 (26) | <0.001 |
|
| ||||||||
| Gestational age, wc | ||||||||
| Mean (SD) | 25.7 (1.8) | 25.8 (1.8) | 25.8 (1.8) | 25.7 (1.8) | 25.7 (1.8) | 25.7 (1.8) | 25.8 (1.8) | 0.11 |
| Category, No. (%) | ||||||||
| 22 | 1550 (4) | 79 (6) | 75 (4) | 358 (5) | 437 (5) | 421 (4) | 334 (4) | |
| 23 | 3133 (9) | 122 (9) | 150 (8) | 660 (9) | 821 (9) | 873 (9) | 779 (9) | |
| 24 | 4762 (14) | 163 (11) | 269 (14) | 871 (12) | 1273 (14) | 1377 (14) | 1241 (14) | |
| 25 | 5361 (15) | 225 (16) | 308 (16) | 1070 (15) | 1397 (15) | 1503 (16) | 1391 (16) | |
| 26 | 5829 (17) | 250 (17) | 333 (17) | 1194 (17) | 1542 (17) | 1580 (16) | 1513 (17) | |
| 27 | 6627 (19) | 283 (20) | 357 (19) | 1337 (19) | 1720 (19) | 1837 (19) | 1733 (20) | |
| 28 | 7374 (21) | 311 (22) | 430 (22) | 1537 (22) | 1942 (21) | 2009 (21) | 1886 (21) | |
|
| ||||||||
| BW, g | ||||||||
| Mean (SD) | 840 (241) | 857 (245) | 847 (241) | 847 (244) | 837 (240) | 836 (241) | 843 (238) | 0.01 |
|
| ||||||||
| Male, No. (%) | 18104 (52) | 748 (52) | 980 (51) | 3657 (52) | 4743 (52) | 5104 (53) | 4600 (52) | 0.82 |
|
| ||||||||
| Small for GA, No. (%)d | ||||||||
| All infants | 2497 (7) | 90 (6) | 135 (7) | 445 (6) | 674 (7) | 722 (8) | 656 (7) | 0.01 |
| By GA, w | ||||||||
| 22 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 23 | 95 (3) | 2 (2) | 9 (6) | 15 (2) | 23 (3) | 32 (4) | 25 (3) | |
| 24 | 275 (6) | 5 (3) | 14 (5) | 36 (4) | 72 (6) | 86 (6) | 81 (7) | |
| 25 | 401 (7) | 15 (7) | 23 (8) | 68 (6) | 109 (8) | 116 (8) | 108 (8) | |
| 26 | 492 (8) | 21 (8) | 34 (10) | 93 (8) | 140 (9) | 130 (8) | 129 (9) | |
| 27 | 554 (8) | 20 (7) | 25 (7) | 102 (8) | 137 (8) | 178 (10) | 137 (8) | |
| 28 | 680 (9) | 27 (9) | 30 (7) | 131 (9) | 193 (10) | 180 (9) | 176 (9) | |
|
| ||||||||
| Major birth defect, No. (%) | 1292 (4) | 50 (3) | 87 (5) | 342 (5) | 283 (3) | 336 (4) | 331 (4) | 0.25 |
Information was missing as follows: mother’s age, 6 infants; prenatal care, 71 infants; maternal diabetes, 66 infants; maternal hypertension, 70 infants; maternal race/ethnicity, 100 infants; gender, 6 infants; small for GA, 6 infants. Infants with black or white maternal race and missing ethnicity were classified as non-Hispanic (2% of blacks, 0.4% of whites). Maternal hypertension was collected as hypertension/pre-eclampsia/eclampsia prior to 2006; beginning 2006 the question was re-worded to ask about hypertension only.
P-values for linear trend across all years were determined by the F or Wald chi-square test from linear or logistic regression models, with adjustment for study center, maternal race/ethnicity, infant gestational age, SGA, and sex except as noted. Models assessing yearly change in maternal race/ethnicity included study center, infant GA, SGA, sex, and year. Models assessing yearly change in GA included study center, maternal race/ethnicity, infant sex, and year. Models assessing yearly change in BW and SGA included study center, maternal race/ethnicity, infant GA, sex, and year. Maternal hypertension, infant GA and small for GA are shown by GA for descriptive purposes only; tests of linear trend were not conducted separately by GA.
Gestational age was assessed using the following hierarchy: (1) by obstetrical measures based on last menstrual period, obstetrical parameters, and/or prenatal ultrasound as recorded in the maternal chart; or (2) by neonatologist’s estimate based on physical criteria, neurologic examination, combined physical and gestational age exam (Ballard or Dubowitz), or examination of the lens.
Small for gestational age was defined as birthweight <10th percentile for age and sex based on Alexander percentiles.9