Table 1 Characteristics of infants in the BWIS dataset
From: Mediation analysis of gestational age, congenital heart defects, and infant birth-weight
| Â | Group | p-value | |
|---|---|---|---|
|  | Cases1 (n = 3362) | Controls (n = 3564) |  |
Dependent and mediating variables | Â | ||
Birth–weight, grams: mean (SD) | 3071 (729) | 3353 (603) | <0.0001 |
Gestational age, weeks: mean (SD) | 38.9 (2.7) | 39.6 (2.2) | <0.0001 |
Covariates | Â | ||
Infant’s sex (%) |  |  |  |
 male | 1661 (49.41) | 1812 (50.84) | 0.2320 |
 female | 1701 (50.59) | 1752 (49.16) |  |
Infant’s race (%) |  |  |  |
 white | 2175 (64.69) | 2358 (66.16) |  |
 African American | 1057 (31.44) | 1108 (31.09) | 0.0274 |
 other | 130 (3.87) | 98 (2.75) |  |
Mother’s age at conception (SD) years | 26.72 (5.92) | 26.27 (5.72) | 0.0014 |
Previous pregnancies (%) | Â | Â | Â |
 never pregnant | 1014 (30.16) | 1154 (32.38) | 0.0006 |
 one | 986 (29.33) | 1154 (30.72) |  |
 two | 661 (19.66) | 709 (19.89) |  |
 ≥ three | 701 (20.85) | 606 (17.00) |  |
Maternal smoking status (%) | Â | Â | Â |
 Non smoker | 2150 (63.95) | 2298 (64.48) | 0.3363 |
 1–10 cigarettes/day | 535 (15.91) | 565 (15.85) |  |
 11–20 cigarettes/day | 480 (14.28) | 526 (14.76) |  |
 21–39 cigarettes/day | 143 (4.25) | 136 (3.82) |  |
 40 or more cigarettes/day | 54 (1.61) | 39 (1.09) |  |
Mother’s education (%) |  |  |  |
 6 years, or less, completion | 26 (0.78) | 22 (0.62) |  |
 7–9 years completion | 220 (6.57) | 228 (6.42) |  |
 10–11 years completion | 358 (10.7) | 405 (11.4) | 0.2248 |
 12 years completion | 1265 (37.8) | 1259 (35.42) |  |
 13 years, or more, completion | 1478 (44.16) | 1640 (46.15) |  |
Pre-pregnancy diabetes (%) | Â | Â | Â |
 No | 3283 (98.09) | 3531 (99.35) | <0.0001 |
 Yes | 64 (1.91) | 23 (0.65) |  |
Method of Delivery | Â | Â | Â |
 Vaginal | 2307 (68.34) | 2694 (75.42) | <0.0001 |
 Caesarian section | 1069 (31.66) | 878 (24.58) |  |