Table 2. Population characteristics for the cohort of pregnancies that resulted in a delivery.

Characteristic	Subcategory	N	(%)
Age at delivery (years)	<20	675	4.8
	20–24	2,231	15.8
	25–29	3,385	23.9
	30–34	4,242	30.0
	35–39	2,852	20.2
	40+	756	5.3
Smoking status*	Non-smoker	7,228	51.1
	Current smoker	4,447	31.4
	Ex-smoker	2,411	17.0
	Unknown	55	0.4
Alcohol drinking status*	Teetotal	1,940	13.7
	Drinks alcohol	9,638	68.2
	Heavy drinker	152	1.1
	Ex-drinker	516	3.6
	Unknown	1,895	13.4
Body mass index*	<20	1,286	9.1
	20–24	4,853	34.3
	25–29	2,754	19.5
	30–34	1,204	8.5
	>34	834	5.9
	Unknown	3,210	22.7
Socioeconomic status(practice level)	Quintile 1– leastdeprived	2,693	19.0
	Quintile 2	2,398	17.0
	Quintile 3	2,862	20.2
	Quintile 4	2,776	19.6
	Quintile 5	3,412	24.1

^*Nearest to pregnancy start date.