An association between maternal CYP1A1 genotype and low birth weight is only observed in the subgroup of babies born to mothers who smoke during pregnancy5
| Maternal smoking status during pregnancy | Maternal CYP1A1 genotype | Number of babies <2500 g | Number of babies ⩾2500 g | Odds ratio (p value)* |
|---|---|---|---|---|
| *p Values calculated using Woolf’s formula for the standard error of the log odds ratio.22 | ||||
| All mothers | AA | 91 | 334 | |
| Aa or aa | 68 | 248 | 1.01 (p = 0.972) | |
| Smoking mothers only | AA | 18 | 57 | |
| Aa or aa | 22 | 27 | 2.58 (p = 0.016) | |