Table 1.
Baseline Characteristics of Paired Infant Samples (n = 210)
| Infant Characteristics | |
| Infant Sex (%) | |
| Female | 89 (42.4) |
| Male | 121 (57.6) |
| Infant Race (%) | |
| White | 197 (93.8) |
| Other | 13 (6.2) |
| Feeding Mode at 6-Week Sample (%) | |
| Breast fed | 157 (74.8) |
| Formula fed | 7 (3.3) |
| Combination | 46 (21.9) |
| Feeding Mode at 1-Year Sample (%) | |
| Breastfed | 70 (33.3) |
| Formula fed | 7 (3.3) |
| Combination | 133 (63.3) |
| Antibiotics During Initial Hospitalization (%) | |
| No | 203 (96.7) |
| Yes | 7 (3.3) |
| Gestational Age at Birth in Weeks [Mean (SD)] | 39.05 (1.56) |
| Birth Weight in Grams [Mean (SD)] | 3414 (507) |
| Age at 6-Week Sample Collection in Days [Mean (SD)] | 46.78 (18.44) |
| Age at 1-Year Sample Collection in Days [Mean (SD)] | 375.32 (35.69) |
| Maternal Characteristics | |
| Delivery Mode (%) | |
| Vaginal | 152 (72.4) |
| Cesarean section | 58 (27.6) |
| Prenatal Antibiotics Prior to Delivery (%) | |
| No | 157 (74.8) |
| Yes | 39 (18.6) |
| Missing | 14 (6.7) |
| Group B Streptococcus Positive (%) | |
| No | 137 (65.2) |
| Yes | 68 (32.4) |
| Missing | 5 (2.4) |
| Parity (%)* | |
| Nulliparous | 104 (49.8) |
| One | 72 (34.4) |
| At least two | 33 (15.8) |
| Intrapartum Antibiotic Exposure Class** (%) | |
| None | 95 (45.2) |
| Penicillin | 43 (20.5) |
| Cephalosporin | 43 (20.5) |
| Multiple | 25 (11.9) |
| Other | 4 (1.9) |
*One mother was missing parity status
**Infants were grouped according to intrapartum antibiotic exposures using the following categories: no antibiotics; penicillin-like antibiotics only (amoxicillins, penicillins); cephalosporins only (cefazolin, cephalexin); multi-drug classes (two or more antibiotics characterized as penicillin, cephalosporin, vancomycin, clindamycin, and/or gentamicin); or “other” antibiotics such as aminoglycosides, glycopeptides, or lincomycin