Table 1

Characteristics of the sample by maternal age

	≤19		20–34		Total		Missing
	n	%	n	%	n	%	n	%	P values
Whole cohort	640	13.9	3951	86.1	4591	100
Ethnicity							14	0.3
Pakistani	107	16.7	1623	41.1	1730	37.7			<0.001
White British	448	70.0	1590	40.2	2038	44.4
Any other ethnicity	85	13.3	724	18.3	809	17.6
Mother’s country of birth							1	0.0
UK and Ireland	564	88.1	2588	65.5	3152	68.7			<0.001
Southeast Asia	41	6.4	984	24.9	1025	22.3
Eastern Europe	15	2.3	135	3.4	150	3.3
Other/unknown	20	3.1	243	6.2	263	5.7
Marital status							9	0.2
Married	87	13.6	2445	61.9	2532	55.2			<0.001
Not married – living with partner	147	23.0	841	21.3	988	21.5
Single	406	63.4	656	16.6	1062	23.1
Parents related other than by marriage							3	0.1
Yes	76	11.9	988	25.0	1064	23.2			<0.001
No	564	88.1	2960	74.9	3524	76.8			<0.001
Highest level of education							14	0.3
Less than 5 GCSEs grades A–C or equivalent	231	36.1	553	14.0	784	17.1			<0.001
5 GCSEs grades A–C or equivalent	298	46.6	1121	28.4	1419	30.9
A-levels or higher	60	9.4	1971	49.9	2031	44.2
Other/unknown	50	7.8	293	7.4	343	7.5
Smoked during pregnancy							7	0.2
Yes	302	47.2	608	15.4	910	19.8			<0.001
No	338	52.8	3336	84.4	3674	80.0			<0.001
Drunk alcohol in the first 3 months of pregnancy							2862	62.3
Yes	185	28.9	698	17.7	883	19.2			0.068
No	140	21.9	702	17.8	842	18.3			0.068
Don’t know	1	0.2	3	0.1	4	0.1
Drunk alcohol since the fourth month of pregnancy							2872	62.6
Yes	89	13.9	478	12.1	567	12.4			0.06
No	233	36.4	916	23.2	1149	25.0			0.06
Don’t know	1	0.2	2	0.1	3	0.1
Used recreational drugs during pregnancy							771	16.8
Yes	29	4.5	47	1.2	76	1.7			<0.001
No	509	79.5	3235	81.9	3744	81.6			<0.001
Used any vitamins or iron supplements in the last 4 weeks							16	0.3
Yes	152	23.8	1610	40.7	1762	38.4			<0.001
No	487	76.1	2326	58.9	2813	61.3			<0.001
BMI category							413	9
Underweight (below 18.5)	59	9.2	199	5.0	258	5.6			<0.001
Healthy weight (18.5–24.9)	368	57.5	1853	46.9	2221	48.4
Overweight (25–29.9)	113	17.7	955	24.2	1068	23.3
Obese (30 or higher)	46	7.2	585	14.8	631	13.7