It is seen that women who smoked had approximately
twice as many low-birth-weight infants per 1000
single live births as women who did not smoke. The differences
are statistically highly significant (p < .00001). (All
statements of significance in this paper are derived by the
x2 test.) There was a regular increase with the number of
cigarettes smoked. The more cigarettes per day the women
smoked, the larger the proportion of low-birth-weight
infants. Women who were past smokers, that is, those who
stopped smoking, were much like those who never
smoked, with respect to the proportion of low-birth-weight
infants. Almost identical relationships were found for
whites and for blacks. These are the striking findings which
corroborate those of a number of other investigators.