Table 1.

Maternal characteristics and child birth weight by the grandmother’s smoking when pregnant with the mother

Characteristic	No (n=34,859)	Yes (n=12,253)	Don’t know (n=4,988)
Maternal age at delivery (Mean (sd))	30.5 (4.4)	30.1 (4.5)	30.6 (4.5)
Maternal parity (%)
Primiparous	49.1	45.0	46.7
1	33.4	36.0	35.1
2	13.7	15.0	14.6
3 or more	3.8	4.1	3.6
Maternal education (%)
Less than high school	4.1	8.7	6.3
High school	23.9	32.9	30.2
Up to 4 years of college	44.4	40.4	41.4
More than 4 years of college	27.5	18.0	22.1
Maternal yearly salary (%)
<200,000 NOK	10.0	10.1	9.4
200,000–400,000 NOK	54.7	57.5	57.3
> 400,000 NOK	35.3	32.4	33.3
Maternal pre-pregnancy BMI (%)
Underweight (<18.5)	3.1	2.5	2.9
Normal weight (18.5–24.9)	69.2	60.3	64.0
Overweight (25–29.9)	20.2	25.0	23.2
Obese (>=30)	7.4	12.3	10.0
Maternal asthma (%)
No	93.4	91.5	91.9
Yes	6.6	8.5	8.1
Maternal smoking during pregnancy (%)
No	95.0	86.1	91.2
Yes	5.0	13.9	8.8
Child birth weight, grams (Mean (sd))	3599 (534)	3626 (555)	3605 (540)

Frequencies based on sample used for current asthma at 36 months classified based on follow-up MoBa questionnaire.

Missing covariate information <2% for each individual covariate.

Given the large sample size, all P-values for chi-square tests (categorical covariates) and ANOVA (continuous covariates) <0.01.