Table 1.

Baseline characteristics of the study population, 2002–2018

Variable	Number of births	Percent	Number of SMM cases	SMM rate per 1000 births
Overall study population	1 048 845	100	18 880	18.00
Maternal age at birth, years
10–14	1330	0.1	35	26.32
15–19	72 579	6.9	1291	17.79
20–24	178 074	17.0	2684	15.07
25–29	342 003	32.6	5324	15.57
30–34	305 898	29.2	5653	18.48
35–39	123 698	11.8	3017	24.39
≥40	25 263	2.4	876	34.68
Gestational age at birth, weeks
20–23	2751	0.3	147	53.44
24–27	4158	0.4	306	73.59
28–33	17 688	1.7	1104	62.42
34–36	59 040	5.6	1966	33.30
37–41	961 322	91.7	15 278	15.89
≥42	3886	0.4	79	20.33
Induced labour	275 262	26.2	5836	21.20
Epidural	655 107	62.5	10 713	16.35
Delivery mode
Vaginal unassisted	579 814	55.3	6386	11.01
Vaginal assisted	156 383	14.9	2724	17.42
Vaginal breech	2328	0.2	95	40.81
Caesarean	310 320	29.6	9675	31.18
Multiple gestations	20 850	2.0	1137	54.53
Stillbirth	3645	0.3	199	54.60
Rurality
Urban	993 282	94.7	17 814	17.93
Rural	55 563	5.3	1066	19.19
Immigration status
Non-immigrant/before 1985	739 252	70.5	13 222	17.89
Immigrated >10 years	62 381	5.9	1165	18.68
Immigrated 5–10 years	62 090	5.9	1249	20.12
Immigrated <5 years	185 122	17.7	3244	17.52
Neighbourhood material deprivation
Quintile 1 (least deprived)	237 877	22.7	4183	17.58
Quintile 2	186 550	17.8	3112	16.68
Quintile 3	189 575	18.1	3327	17.55
Quintile 4	191 376	18.2	3423	17.89
Quintile 5 (most deprived)	226 337	21.6	4397	19.43
Missing	17 130	1.6	438	25.57

N=1 048 845 births.