Table 5.

Maternal demographic and birth-related characteristics by linkage group for liveborn singleton pregnancies, NSW 2001-2008

Variable	Birth-hospital record linked groups			Unlinked groups
	Mothers and infants	Mothers only	Infants only	Birth records	Hospital records
	N = 667315	N = 11312	N = 9553	N = 3017	N = 8145
	n (%)	n (%)	n (%)	n (%)	n (%)
Maternal age
< 25	122 417 (18.3)	2 837 (25.1)	1 870 (19.6)	418 (13.9)	1 691 (20.7)
26-34	407 468 (61.1)	6 418 (56.7)	5 779 (60.5)	1 916 (63.5)	4 753 (58.3)
35+	137 304 (20.6)	2 055 (18.2)	1 851 (19.4)	679 (22.5)	1 716 (21.0)
Marital status (Married)	546 152 (81.8)	8 167 (72.2)	- (-)	- (-)	6 343 (77.7)
Parity
0	277 713 (41.6)	5 077 (44.9)	3 994 (41.8)	1 378 (45.7)	- (-)
1	224 843 (33.7)	3 561 (31.5)	2 879 (30.1)	976 (32.4)	- (-)
2	102 521 (15.4)	1 533 (13.6)	1 410 (14.7)	390 (12.9)	- (-)
3+	61 127 (9.2)	1 123 (9.9)	1 248 (13.1)	255 (8.5)	- (-)
Australian born mother	478 317 (71.7)	7 458 (65.9)	6 847 (71.7)	2 233 (74.0)	5 740 (70.3)
Social disadvantage
1 (Least)	140 069 (21.0)	2 711 (24.0)	1 835 (19.2)	919 (30.5)	2 044 (25.1)
2-4	367 930 (55.1)	5 596 (49.5)	5 143 (53.8)	1 463 (48.5)	4 084 (50.1)
5 (Greatest)	158 193 (23.7)	2 918 (25.8)	2 483 (26.0)	592 (19.6)	2 030 (24.9)
Smoked during pregnancy	95 866 (14.4)	2 225 (19.7)	1 904 (19.9)	374 (12.4)	- (-)
Antenatal care ≥ 15 weeks	164 940 (24.7)	3 416 (30.2)	2 598 (27.2)	616 (20.4)	- (-)
Diabetes	34 760 (5.2)	531 (4.7)	428 (4.5)	115 (3.8)	385 (4.7)
Hypertension	50 582 (7.6)	760 (6.7)	490 (5.1)	157 (5.2)	551 (6.8)
Placental abruption	2 555 (0.4)	68 (0.6)	- (-)	- (-)	35 (0.4)
Placenta praevia	3 595 (0.5)	56 (0.5)	- (-)	- (-)	127 (1.6)
Induction of labour	166 647 (25.0)	2 633 (23.3)	2 146 (22.5)	739 (24.5)	1 465 (18.0)
Delivery by caesarean	179 528 (26.9)	3 189 (28.2)	2 028 (21.2)	906 (30.0)	2 136 (26.2)
Duration of pregnancy < 26 weeks	1 166 (0.2)	92 (0.8)	21 (0.2)	13 (0.4)	68 (0.8)
Birth in private hospital	168 036 (25.2)	3 486 (30.8)	1 939 (20.3)	1 731 (57.4)	2 047 (25.1)