Table 3.

Association of the grandmother’s and the mother’s smoking during pregnancy with asthma development in the grandchild

Outcome	Exposure	n, total	n, cases	Crude RR(95% CI)	Adj RR(95% CI)a
Asthma at 36 months (N=53,169)	Mother and grand maternal smoking during pregnancy
	Neither	32,701	1,735	1	1
	Only grandmother	10,411	686	1.24 (1.14, 1.35)	1.15 (1.06, 1.26)
	Only mother	1,728	106	1.15 (0.94, 1.41)	1.06 (0.87, 1.30)
	Both grandmother and mother	1,685	117	1.32 (1.10, 1.59)	1.15 (0.95, 1.40)
Asthma at 7 years (N=25,394)	Mother and grand maternal smoking during pregnancy
	Neither	15,426	708	1	1
	Only grandmother	4,973	299	1.32 (1.16, 1.50)	1.23 (1.08, 1.40)
	Only mother	858	49	1.30 (1.00, 1.70)	1.17 (0.89, 1.53)
	Both grandmother and mother	775	49	1.42 (1.09, 1.87)	1.22 (0.92, 1.60)
Use of asthma medications at 7 years based on prescription registry (N=45,607)	Mother and grand maternal smoking during pregnancy
	Neither	26,600	1,157	1	1
	Only grandmother	9,172	483	1.22 (1.10, 1.35)	1.14 (1.03, 1.26)
	Only mother	2,180	122	1.27 (1.06, 1.53)	1.11 (0.92, 1.34)
	Both grandmother and mother	2,181	143	1.49 (1.26, 1.76)	1.25 (1.05, 1.49)

Adjusted for maternal age, maternal parity, maternal education, maternal salary, maternal pre-pregnancy BMI, and maternal asthma.

Multiple imputation of missing covariate information by chained equations conducted for all measures of association presented.

^*Values for the respondents reporting “don’t know” to the grandmother’s smoking when pregnant with the mother were imputed using multiple imputation together with all other missing covariate information. There were a total of 6,097 children in the analysis of asthma at 36 months, 2,884 children in the analysis of asthma at 7 years and 5,474 children in the analysis of use of asthma medication in the prescription database for whom we imputed missing information on the combined exposure of both grandmother and mother smoking during pregnancy.