Including mother fixed effects, which controls for unobserved characteristics of the mother, reduces the estimated effects of smoking considerably, though they remain large: being a smoker is estimated to reduce birth weight by 38.9 g, and each cigarette reduces it a further 2.2 g for a total reduction of about 61 g in infants of women who smoke 10 cigarettes per day.
Hence it would take a roughly 3.7 unit change in mean CO levels to have an equivalent impact on birth weight as that from smoking 10 cigarettes per day.
Similarly, the effect of smoking 10 cigarettes per day is a bit more than twice as large as the impact of a one unit change
in mean CO in terms of the effect on the incidence of low birth weight.