Table 1

Selected maternal characteristics for infants by preterm birth (PTB)* and small-for-gestational age (SGA) status,† National Birth Defects Prevention Study, 1997–2009

 PTBNon-PTBp Value‡SGANon-SGAp Value‡
n (%)n (%)n (%)n (%)
Total§474 (8.0)5452 (92.0)452 (7.8)5378 (92.3)
Maternal age (years)
 <2037 (7.8)364 (6.7)0.0130 (6.6)369 (6.9)0.002
 20–24112 (23.6)1263 (23.2)130 (28.8)1221 (22.7)
 25–29150 (31.7)1567 (28.7)122 (27.0)1561 (29.0)
 30–3494 (19.8)1489 (27.3)92 (20.4)1467 (27.3)
 ≥3581 (17.1)769 (14.1)78 (17.3)760 (14.1)
 Missing0000
Race/ethnicity
 Non-Hispanic White272 (57.5)3526 (64.7)0.001282 (62.4)3459 (64.3)0.001
 Non-Hispanic Black80 (16.9)608 (11.2)32 (7.1)646 (12.0)
 Hispanic87 (18.4)946 (17.4)96 (21.2)915 (17.0)
 Other34 (7.2)371 (6.8)42 (9.3)358 (6.7)
 Missing1100
Education (years)
 <1256 (11.8)528 (9.7)0.0355 (12.2)516 (9.6)0.001
 12129 (27.2)1261 (23.1)123 (27.2)1242 (23.1)
 13–15145 (30.6)1683 (30.9)149 (33.0)1643 (30.6)
 ≥16144 (30.4)1977 (36.3)125 (27.7)1974 (36.7)
 Missing0303
Parity
 0219 (46.3)2445 (44.9)0.54193 (42.7)2435 (45.3)0.29
 ≥1254 (53.7)3006 (55.2)259 (57.3)2943 (54.7)
 Missing1100
Body mass index (kg/m2)
 Underweight (<18.5)25 (5.3)250 (4.7)0.3436 (8.3)233 (4.4)<0.001
 Normal (18.5–24.9)241 (51.5)2895 (54.3)258 (59.2)2829 (53.6)
 Overweight (25.0–29.9)107 (22.9)1268 (23.8)83 (19.0)1271 (24.1)
 Obese (≥30)95 (20.3)923 (17.3)59 (13.5)942 (17.9)
 Missing611616103
Pregestational diabetes
 No467 (98.5)5411 (99.4)0.03450 (99.6)5334 (99.3)0.54
 Yes7 (1.5)34 (0.6)2 (0.4)37 (0.7)
 Missing0707
High blood pressure
 No355 (74.9)4766 (87.5)<0.001367 (81.2)4668 (86.9)0.001
 Yes119 (25.1)680 (12.5)85 (18.8)704 (13.1)
 Missing0606
Folic acid use¶
 No204 (43.0)2435 (44.7)0.49228 (50.4)2371 (44.1)0.01
 Yes270 (57.0)3017 (55.3)224 (49.6)3007 (55.9)
 Missing0000
Alcohol use**
 No300 (63.7)3093 (56.9)0.004255 (57.1)3064 (57.1)0.98
 Yes171 (36.3)2343 (43.1)192 (43.0)2300 (42.9)
 Missing316514
Smoking**
 No377 (79.5)4421 (81.1)0.40344 (76.1)4368 (81.2)0.01
 Yes97 (20.5)1030 (18.9)108 (23.9)1009 (18.8)
 Missing0101
Hours worked per week††,‡‡
 <40167 (35.3)2008 (37.0)0.71163 (36.2)1963 (36.6)0.86
 40204 (43.1)2244 (41.3)184 (40.9)2230 (41.6)
 >40102 (21.6)1180 (21.7)103 (22.9)1167 (21.8)
 Missing120218
  • *Excluded non-working mothers, multiple gestations and mothers whose reported job did not match job codes available in Occupational Information Network (O*NET), V.9.0.

  • †For the SGA analysis, we further excluded infants with missing birth weight or weighed <500 g; missing infant sex, race or maternal parity, or fell outside of calculated fetal growth curves.

  • ‡χ2 tests.

  • §Percentages in this row are horizontal, while other percentages are across columns.

  • ¶One month before conception through the first month of pregnancy.

  • **One month before conception through the third month of pregnancy.

  • ††Based on primary job.

  • ‡‡Jobs with<1 or >168 hours worked per week were considered missing.