Placental ratio in white and black women: relation to smoking and anemia.

In a study of 7,000 pregnancies it was found that, particularly in black women, hemoglobin levels were lower in smokers than in nonsmokers. This is the reverse of previously reported findings in nonpregnant persons. At delivery, the mean ratio of placental weight to birth weight (placental ratio) was higher in the infants of smokers than of nonsmokers. This observation is discussed in the light of reported elevated placental ratios at high altitudes or after severe anemia of pregnancy. The relationships are complex, and are not uniform with respect to ethnic group.