Table 1.

Demographic characteristics

	Antibiotic-naïve group (n=46)	Antibiotic-exposed group (n=22)	p-values
Birth weight in g, median (range)	1478.0 (688–1940)	1173.0 (648–1924)	0.003
Gestational age in weeks, median (range)	31.5 (28–35)	28.5 (24–32)	<0.001
Female gender, n (%)	25 (54.3)	12 (54.5)	0.988
Multiple gestations, n (%)	35 (76.1)	17 (77.3)	0.914
Race, n (%)
White	23 (50.0)	11 (50.0)	1
Black or African American	18 (39.1)	10 (45.5)	0.62
Asian	2 (4.3)	0 (0.0)	0.321
Native Hawaiian or other Pacific Islander	1 (2.2)	0 (0.0)	0.486
Unknown or not reported	2 (4.3)	1 (4.5)	0.97
Hispanic or Latino, n (%)	2 (4.3)	1 (4.5)	0.97
Cesarean section, n (%)	42 (91.3)	20 (90.9)	0.957
Diet, n (%)
Mostly breast milk	39 (84.8)	19 (86.4)	0.863
Any receipt of formula	4 (8.7)	1 (4.5)	0.54
Any receipt of breast milk	44 (95.7)	22 (100.0)	0.321
Perinatal maternal antibiotic exposure, n (%)	39 (84.8)	20 (90.9)	0.486
Specimen collection time in days
Week 1	7 (5–9)	6.5 (5–9)	0.907
Week 3	16 (15–21)	17 (15–24)	0.562