Table 1.

Maternal characteristics of the study population

	Women who used codeine during pregnancy; exposed group (n = 2,666)		Women who did not use opioids during pregnancy: unexposed group (n = 65,316)
	No.	%	No.	%
Maternal age (years)
< 20	32	1.2	714	1.1
20 – 29	1,194	44.8	28,840	44.1
30 – 39	1,380	51.8	34,530	52.9
≥ 40	60	2.2	1,234	1.9
Parity
0	1,153	43.2	28,523	43.7
≥1	1,513	56.7	36,787	56.3
Plurality
1	2,611	97.9	64,123	98.2
> 1	55	2.1	1,193	1.8
Ethnicity
Of Norwegian descent	2,572	96.5	61,782	94.6
Not of Norwegian descent	94	3.5*	3,534	5.4
Marital status
Married/cohabiting	2,553	95.8	63,484	97.2
Other	113	4.2*	1,832	2.8
Education
Primary	80	3.0	1623	2.5
Secondary	1,005	37.7	20,803	31.8
Tertiary	1,525	57.2*	41,607	63.4
BMI prior to pregnancy (kg/m2)
< 18.5	65	2.4	2,002	3.1
18.5 – 25.0	1,479	55.5	41,930	64.2
> 25.0	1,050	39.4*	19,483	29.8
Folic acid intake prior to pregnancy	596	22.3	15,041	23.0
Sick leave lasting longer than 2 weeks during pregnancy	1,023	38.4*	20,505	31.4
Smoking at gestational week 30	391	14.7*	6,180	9.4
Alcohol intake during pregnancya	1,421	53.3**	3,3512	51.3

Some data do not add up to the total due to missing values

^* Pearson’s χ² test P < 0.001 when compared with the unexposed control group,

^** Pearson’s χ² test P < 0.05 when compared with the unexposed control group

^a Including data on sporadic intake and intake before the women were aware of their pregnancy