Table 1

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

CharacteristicNo
(n=34 859)
Yes
(n=12 253)
Don't know
(n=4988)
Maternal age at delivery (mean (SD))30.5 (4.4)30.1 (4.5)30.6 (4.5)
Maternal parity (%)
 Primiparous49.145.046.7
 133.436.035.1
 213.715.014.6
 3 or more3.84.13.6
Maternal education (%)
 Less than high school4.18.76.3
 High school23.932.930.2
 Up to 4 years of college44.440.441.4
 More than 4 years of college27.518.022.1
Maternal yearly salary (%)
 <200 000 NOK10.010.19.4
 200 000–400 000 NOK54.757.557.3
 >400 000 NOK35.332.433.3
Maternal pre-pregnancy BMI (%)
 Underweight (<18.5)3.12.52.9
 Normal weight (18.5–24.9)69.260.364.0
 Overweight (25–29.9)20.225.023.2
 Obese (≥30)7.412.310.0
Maternal asthma (%)
 No93.491.591.9
 Yes6.68.58.1
Maternal smoking during pregnancy (%)
 No95.086.191.2
 Yes5.013.98.8
Child birth weight, g (mean (SD))3599 (534)3626 (555)3605 (540)
  • Frequencies based on sample used for current asthma at 36 months classified based on follow-up Norwegian Mother and Child Cohort Study (MoBa) questionnaire.

  • Missing covariate information <2% for each individual covariate.

  • Given the large sample size, all p values for χ2 tests (categorical covariates) and analysis of variance (continuous covariates) <0.01.