Table 1:

Maternal and infant characteristics of very preterm infants admitted to neonatal intensive care units in Canada, 2004–2017

Characteristic	No. (%) of infants^*			p value for epochs^†	p value for linear trend^‡

	Epoch 1 (2004–2008) n = 15 060^*	Epoch 2 (2009–2012) n = 15 692^*	Epoch 3 (2013–2017) n = 20 079^*
Maternal

Age, yr, mean ± SD	30.2 ± 6.0	30.7 ± 5.9	31.3 ± 5.8	< 0.001	< 0.001

Hypertension	n = 14 750	n = 15 200	n = 19 524	0.07	0.1
	2676 (18.1)	2912 (19.2)	3681 (18.9)

Prenatal care	n = 14 440	n = 14 577	n = 19 307	< 0.001	< 0.001
	14 080 (97.5)	14 314 (98.2)	18 702 (96.9)

Chorioamnionitis	n = 13 678	n = 12 183	n = 14 758	< 0.001	< 0.001
	1764 (12.9)	2115 (17.4)	3081 (20.9)

Infant

Gestational age, wk, median (IQR)	29 (27–31)	30 (27–31)	30 (27–31)	0.9	> 0.9

Gestational age group, wk				< 0.001

23–25	1729 (11.5)	1906 (12.1)	2630 (13.1)

26–28	4101 (27.2)	4014 (25.6)	5042 (25.1)

29–32	9230 (61.3)	9772 (62.3)	12 407 (61.8)

Birth weight, g, mean ± SD	1324 ± 451	1328 ± 454	1325 ± 454	0.7	0.8

Sex, male	n = 15 036	n = 15 671	n = 20 054	0.005	0.02
	8031 (53.4)	8645 (55.2)	10 989 (54.8)

Singleton	n = 15 008	n = 15 683	14 038 (69.9)	0.001	0.02
	10 338 (68.9)	10 679 (68.1)

Small for gestational age	n = 15 037	n = 15 680	n = 20 059	0.6	0.3
	1429 (9.5)	1530 (9.8)	1971 (9.8)

Minor congenital malformation	2423 (16.1)	2472 (15.8)	3249 (16.2)	0.5	0.8

SNAP-II score > 20	n = 15 051	n = 15 546	n = 19 900	< 0.001	< 0.001
	2690 (17.9)	2527 (16.3)	2954 (14.8)

Note: IQR = interquartile range, SD = standard deviation, SNAP = Score for Neonatal Acute Physiology.
↵* Unless stated otherwise.
↵† The p value for differences between the 3 epochs were obtained using the χ² test for categorical variables and F test or Kruskal–Wallis test as appropriate.
↵‡ The p value for linear trend was for 2004–2017. Significance was assessed using the F or Wald χ² test from linear or logistic regression models using 1-year periods as an independent continuous variable.