Table 2

Rate of hospital usage in preterm infants postdischarge from birth admission to 11 months by sociodemographic characteristics, 2010–2011

Characteristics	Events	Time at risk	(Events/risk)×1000	Unadjusted IRR (95% CI)	p Value	aIRR (95% CI)*	p Value
All-cause hospitalisations postdischarge from birth admission to 11 months
Infant
Indigenous status
Indigenous	745	152 285	4.89	1.44 (1.28 to 1.62)	<0.001	1.24 (1.08 to 1.42)	0.002
Non-Indigenous	4539	1 335 534	3.40	1.00		1.00
Prematurity† (week)
<28	340	54 951	6.19	1.95 (1.74 to 2.19)	<0.001	1.91 (1.70 to 2.13)	<0.001
28<32	598	103 070	5.80	1.76 (1.61 to 1.93)	<0.001	1.73 (1.59 to 1.88)	<0.001
32<37	4346	1 329 798	3.27	1.00		1.00
Child sex
Male	3036	818 577	3.71	1.10 (1.04 to 1.17)	0.002	1.16 (1.09 to 1.24)	<0.001
Female	2248	669 242	3.36	1.00		1.00
Birth weight
Low birth weight (<2500 g)	3212	685 424	4.69	1.84 (1.72 to 1.96)	<0.001	1.83 (1.72 to 1.96)	<0.001
Normal birth weight (≥2500 g)	2072	802 395	2.58	1.00		1.00
SGA index
SGA (<10th centile)	576	116 067	4.96	1.42 (1.26 to 1.59)	<0.001	1.41 (1.26 to 1.58)	<0.001
AGA (10th–90th centile)	4226	1 196 920	3.53	1.00		1.00
LGA (>90th centile)	482	172 420	2.80	0.79 (0.72 to 0.86)	<0.001	0.78 (1.26 to 1.58)	<0.001
APGAR 5 score
<7 (abnormal)	396	87 068	4.55	1.33 (1.18 to 1.50)	<0.001	0.94 (0.83 to 1.06)	0.322
≥7 (healthy)	4885	1 400 390	3.49	1.00		1.00
Maternal
Maternal age (years)
<20	372	86 080	4.32	1.22 (1.06 to 1.42)	0.007	1.15 (0.99 to 1.34)	0.060
20–24	853	237 825	3.59	1.02 (0.93 to 1.13)	0.664	0.98 (0.88 to 1.08)	0.633
25–29	1378	393 858	3.50	1.00		1.00
30–34	1459	427 127	3.42	0.98 (0.90 to 1.07)	0.704	1.00 (0.92 to 1.09)	0.987
35+	1222	342 931	3.56	1.03 (0.95 to 1.12)	0.444	0.99 (0.91 to 1.08)	0.865
Gravidity
0	1658	479 189	3.46	0.98 (0.90 to 1.06)	0.572	0.89 (0.82 to 0.97)	0.009
1	1323	396 837	3.33	0.94 (0.86 to 1.03)	0.186	0.91 (0.83 to 0.99)	0.039
2	924	261 034	3.54	1.00		1.00
≥3	1379	350 759	3.93	1.12 (1.01 to 1.24)	0.033	1.02 (0.92 to 1.12)	0.770
Area
Socioeconomic status
Most disadvantaged 1	467	103 279	4.52	1.34 (1.12 to 1.59)	0.001	1.11 (0.95 to 1.30)	0.183
2	793	227 854	3.48	1.04 (0.92 to 1.16)	0.553	0.98 (0.86 to 1.11)	0.742
3	665	190 211	3.50	1.03 (0.91 to 1.17)	0.597	0.98 (0.89 to 1.08)	0.679
4	1444	404 092	3.57	1.06 (0.95 to 1.17)	0.287	1.02 (0.93 to 1.13)	0.619
Least disadvantaged 5	1776	525 038	3.38	1.00		1.00
Geographic location
Major city	2089	635 695	3.29	1.00		1.00
Inner regional	1982	552 517	3.59	1.09 (1.02 to 1.17)	0.012	1.07 (1.01 to 1.14)	0.017
Outer regional	507	115 243	4.40	1.34 (1.18 to 1.52)	<0.001	1.24 (1.09 to 1.41)	0.001
Remote	128	40 877	3.13	0.95 (0.80 to 1.13)	0.569	0.95 (0.81 to 1.13)	0.574
Very remote	439	106 142	4.14	1.27 (1.05 to 1.54)	0.014	1.09 (0.92 to 1.29)	0.330
All-cause emergency department presentations postdischarge from birth admission to 11 months
Infant
Indigenous status
Indigenous	1257	152 285	8.25	2.20 (1.94 to 2.49)	<0.001	1.71 (1.44 to 2.02)	<0.001
Non-Indigenous	4400	1 335 534	3.29	1.00		1.00
Prematurity† (week)
<28	295	54 951	5.37	1.47 (1.23 to 1.76)	<0.001	1.48 (1.25 to 1.76)	<0.001
28<32	526	103 070	5.10	1.36 (1.21 to 1.52)	<0.001	1.36 (0.21 to 1.53)	<0.001
32<37	4836	1 329 798	3.64	1.00		1.00
Child sex
Male	3327	818 577	4.06	1.16 (1.09 to 1.25)	<0.001	1.20 (1.11 to 1.29)	<0.001
Female	2330	669 242	3.48	1.00		1.00
Birth weight
Low birth weight (<2500 g)	2821	685 423	4.12	1.18 (1.09 to 1.27)	<0.001	1.16 (1.06 to 1.26)	0.001
Normal birth weight (≥2500 g)	2836	802 395	3.53	1.00		1.00
SGA index
SGA (<10th centile)	523	116 067	4.51	1.19 (1.03 to 1.39)	0.020	1.19 (1.02 to 1.38)	0.024
AGA (10th–90th centile)	4491	1 196 920	3.75	1.00		1.00
LGA (>90th centile)	643	172 419	3.73	0.95 (0.82 to 1.09)	0.426	0.97 (0.84 to 1.12)	0.698
APGAR 5 score
<7 (abnormal)	343	87 067	3.94	1.05 (0.90 to 1.23)	0.541	0.92 (0.78 to 1.08)	0.295
≥7 (healthy)	5312	1 400 390	3.79	1.00		1.00
Maternal
Maternal age (years)
<20	538	86 080	6.25	1.53 (1.29 to 1.81)	<0.001	1.51 (1.22 to 1.87)	<0.001
20–24	1309	237 825	5.50	1.39 (1.23 to 1.56)	<0.001	1.37 (1.20 to 1.56)	<0.001
25–29	1462	393 858	3.71	1.00		1.00
30–34	1360	427 127	3.18	0.90 (0.81 to 1.00)	0.060	0.92 (0.81 to 1.05)	0.231
35+	988	342 931	2.88	0.82 (0.73 to 0.92)	0.001	0.80 (0.70 to 0.91)	0.001
Gravidity
0	1620	479 189	3.38	0.91 (0.79 to 1.04)	0.153	0.82 (0.70 to 0.95)	0.010
1	1437	396 836	3.62	0.97 (0.84 to 1.11)	0.642	0.92 (0.78 to 1.07)	0.278
2	990	261 034	3.79	1.00		1.00
≥3	1610	350 759	4.59	1.16 (1.00 to 1.35)	0.047	1.14 (0.98 to 1.33)	0.089
Area
Socioeconomic status
Most disadvantaged 1	809	103 279	7.83	2.46 (1.93 to 3.14)	<0.001	1.61 (1.30 to 2.00)	<0.001
2	796	227 854	3.49	1.17 (0.92 to 1.49)	0.199	1.04 (0.86 to 1.25)	0.679
3	838	190 211	4.41	1.39 (1.06 to 1.80)	0.016	1.25 (1.03 to 1.51)	0.023
4	1464	404 092	3.62	1.14 (0.89 to 1.47)	0.302	1.09 (−0.89 to 1.34)	0.402
Least disadvantaged 5	1603	525 038	3.05	1.00		1.00
Geographic location
Major city	1881	635 695	2.96	1.00		1.00
Inner regional	1976	552 517	3.58	1.26 (1.06 to 1.49)	0.008	1.11 (0.97 to 1.27)	0.137
Outer regional	624	115 243	5.41	1.82 (1.48 to 2.24)	<0.001	1.48 (1.26 to 1.75)	<0.001
Remote	202	40 877	4.94	1.70 (1.27 to 2.26)	<0.001	1.39 (1.06 to 1.84)	0.018
Very remote	827	106 142	7.79	2.72 (2.20 to 3.37)	<0.001	1.82 (1.49 to 2.22)	<0.001

*Adjusted for Indigenous status, socioeconomic status, maternal age, gravidity, gender of child, birth weight.
†Prematurity was not adjusted for birth weight due to collinearity.
AGA, appropriate for gestational age; IRR, incident rate ratio; aIRR, adjusted incident rate ratio; LGA, large for gestational age; SGA, small for gestational age.