Table III.

Distribution of infant demographics and clinical characteristics among quartiles of year instrumental variable (data are expressed as column percentages unless otherwise noted)

	Quartile of year instrumental variable
	1	2	3	4
	N=9478	N=9157	N=9144	N=9203
Median percentage of infants exposed to furosemide	5	7	9	12
Gestational age, weeks
23–25	29	31	33	31
26–27	38	34	37	38
28–29	33	34	30	31
Birth weight, grams
500–749	29	30	32	32
750–999	40	39	41	41
1000–1249	31	31	28	28
Small for gestational age	14	14	14	15
Cesarean section	74	74	74	72
Prenatal steroids	84	82	77	76
Inborn	87	86	86	86
5-minute Apgar score
0–3	8	7	6	5
4–6	24	24	24	22
7–10	68	69	69	73
Male	51	53	52	53
Race/ethnicity
White	46	49	47	49
Black	31	31	31	28
Hispanic	22	20	22	23
Percentage risk of BPD/death on postnatal day 7a, median	44	47	53	55
Ventilator status on postnatal day 7
High-frequency	15	16	17	14
Conventional	24	28	34	41
CPAP	44	31	23	19
NC/hood	14	20	22	20
None	3	4	5	6
Fractional inspired oxygen on postnatal day 7
21%	57	56	49	42
22–50%	41	42	47	53
51–99%	2	2	3	4
100%	0.7	0.9	1.0	1.6
Received dexamethasone	16	17	19	21
Atrial septal defect or ventricular septal defect	10	8	7	6
Patent ductus arteriosus surgery	8	12	16	18

^aRefers to estimated risk of BPD or death at postnatal day 7 according to a model developed by the National Institute of Child Health and Human Development Neonatal Research Network (16, 17).

BPD, bronchopulmonary dysplasia; CPAP, continuous positive airway pressure ventilation