Associations Between Smoking During Pregnancy and Offspring ADHD Diagnoses Examined With 4 Separate Cox Proportional Hazard Analyses

No. of Person-Months at Observed RiskbNo. of CasesIncidence RatecHazard RatioSE95% CIPHazard RatioSE95% CIPn
1. Maternal smokingNo6 956 115138719.9Ref Ref
Yes642 99636356.52.300.142.05–2.59<.0011.480.101.30–1.68<.00192 499
2. Paternal smokingNo5 835 047108518.6Ref Ref
Yes1 903 56668936.21.760.091.60–1.93<.0011.280.071.16–1.42<.00194 256
3. Grandmother smoked when pregnant with motherNo4 940 11893819.0Ref Ref
Yes1 874 92560332.21.640.091.48–1.82<.0011.280.071.15–1.42<.00182 944
4. Mother smoked in previous pregnanciesdNo4 239 52178118.4Ref Ref
Yes778 48936346.–2.51<.0011.530.111.33–1.75<.00161 069
  • Separate analyses were performed for each of the 4 smoking variables so that the associations between each of them and offspring ADHD are not controlled for each other. CI, confidence interval; Ref, reference group to which smokers are compared.

  • a Adjusted for the following covariates: maternal and paternal age, maternal and paternal education, maternal and paternal ADHD symptoms, maternal (prepregnancy) and paternal BMI, maternal alcohol consumption during pregnancy, parity, child’s birth year, and geographical region.

  • b Observation period between January 2008 and December 2014 for participants born in or before January 2008.

  • c Per 100 000 person-months under observed risk.

  • d Only applicable to women who had been pregnant before.