Table 1.

Sample characteristics across levels of maternal cigarette smoking in pregnancy.

	Average number of cigarettes per day			Total	P b
	0	1–9	10+a
Number of participants	1276	263	243	1,782
Timing of interview (gestational week)	17.0 (13.0/24.0)	16.0 (12.0/24.0)	17.0 (13.0/24.0)	17.0 (13.0/24.0)	0.608
Median number of cigarettes	0	5	13	0
Maternal age (years); mean (SD)	31.0 (4.2)	30.2 (4.9)	30.5 (4.8)	30.8 (4.4)	0.019
Parity
0 (%)	50.6	51.5	51.9	50.9	0.800
1 (%)	32.3	33.7	29.2	32.1
2+ (%)	17.1	14.8	18.9	17.0
Maternal Body Mass Index (kg/m2)	22.7 (19.6/29.0)	22.5 (19.7/28.4)	22.3 (19.2/28.4)	22.6 (19.6/28.7)	0.810
Single mother (%)	9.7	15.9	22.8	12.4	0.000
Parental education (years)	13.0 (11.0/16.5)	12.5 (10.5/15.5)	12.0 (10.5/14.5)	13.0 (11.0/16.0)	0.000
Suboptimal home environment (%)	14.6	25.0	37.3	19.2
Maternal IQ; mean (SD)	101.6 (14.8)	96.6 (14.8)	95.2 (14.7)	100.0 (15.0)	0.000
Maternal alcohol consumption in pregnancy (%)	52.8	50.8	51.0	52.3	0.760
Paternal prenatal smoking (%)	23.4	57.1	64.9	33.8	0.000
Parental postnatal smoking (%)	16.4	68.6	76.3	32.3	0.000
Child's sex (male, %)	53.4	48.1	47.7	51.8	0.125
Age at testing (years)	5.2 (5.1/5.3)	5.2 (5.1/5.3)	5.2 (5.1/5.3)	5.2 (5.1/5.3)	0.551
Birth weight (grams)	3649.0 (513.1)	3546.4 (492.9)	3424.1 (508.8)	3603.2 (515.5)	0.000
Gestational age (days)	282.0 (268.0/293.0)	282.0 (267.0/292.0)	280.0 (267.0/294.0)	281.0 (267.0/293.0)	0.229
Breast feeding ≤ 1 month (%)	12.7	15.8	21.1	14.3	0.004
Condition/medicine (%)	2.7	3.4	5.3	3.2	0.104
Impaired hearing (%)	4.6	4.2	7.0	4.8	0.229
Impaired vision (%)	2.4	2.3	7.8	3.1	0.000

Data are presented as medians (10/90 percentiles), unless otherwise specified.

^aRange 10–25 cigarettes/day.

^b P values for unweighted data.