Figure 5 shows that the distribution by weeks of gestation
was approximately the same for infants of smoking
and non-smoking mothers for both whites and blacks.
Apparently, therefore, there has not been a displacement as
far as length of pregnancy is concerned. Moreover, the
mean birth weight of infants of smoking mothers was
lower than that of nonsmoking mothers over the entire
span of the gestational age distribution (table 6). Infants of
smoking mothers weighed approximately 200 grams less
than those of nonsmoking mothers. The difference was of
about the same order of magnitude in nearly each week of
gestation.