Table 1

Baseline characteristics of live born singletons (total N=.1 018 136)

	n	%
Mother’s age at childbirth (years)
<20	44 486	4.4
20–24	181 633	17.8
25–29	253 055	24.9
30–34	293 741	28.9
35–39	193 622	19.0
40+	51 599	5.1
Parity
Nulliparous	480 616	47.2
Parous	496 203	48.7
Missing	41 317	4.1
Mother’s marital status
Married	581 160	57.1
Partner	347 366	34.1
Single	89 610	8.8
Mother’s country of birth
Non-UK	225 695	22.2
UK	791 012	77.7
Missing	1429	0.1
Index of Multiple Deprivation*
Least deprived Q1	276 838	27.2
Q2	216 006	21.2
Q3	180 300	17.7
Q4	161 793	15.9
Most deprived Q5	157 195	15.4
Missing	26 004	2.6
Sex
Male	521 169	51.2
Female	496 967	48.8
Ethnicity (child)
White British	677 236	66.5
White other	59 683	5.9
Bangladeshi	14 546	1.4
Indian	27 783	2.7
Pakistani	41 739	4.1
Black African	34 571	3.4
Black Caribbean	12 410	1.2
Other	91 570	9.0
Missing	58 598	5.8
Gestational age (weeks)
<28	1730	0.2
28–29	2089	0.2
30–31	3227	0.3
32	2656	0.3
33	4050	0.4
34	7292	0.7
35	11 663	1.1
36	23 346	2.3
37	54 001	5.3
38	137 926	13.5
39	231 376	22.7
40	288 065	28.3
41	208 757	20.5
42	41 958	4.1
Small for gestational age at birth
No	918 419	90.2
Yes	99 717	9.8
Mode of birth
Vaginal	751 653	73.8
Caesarean section	222 615	21.9
Missing	43 868	4.3
Labour induction
No	626 178	61.5
Yes	154 851	15.2
Missing	237 107	23.3
Season of birth
Jan–Mar	236 944	23.3
Apr–Jun	254 016	24.9
Jul–Sep	270 282	26.5
Oct–Dec	256 894	25.2

*The Index of Multiple Deprivation (IMD) is the official measure of relative deprivation for small areas (or neighbourhoods) in England.