Gross differences observed in the placentas of smokers and nonsmokers.

Gross placental characteristics of 7651 smokers and nonsmokers are compared in light of the previous finding that placentas of smokers are heavier for the weight of their fetuses than are those of nonsmokers. Subchorionic fibrin deposits and placental calcification are more prevalent in the placentas of smokers than in those of nonsmokers. While mean placental weights and placental weight distributions for light and heavy smokers combined do not differ from those of nonsmokers, other placental measurements do differ. Smokers have thinner, rounder placentas than nonsmokers and the distance from the edge of rupture of the membranes to the placental margin is reduced among smokers. These findings are discussed in relation to placental changes observed at high altitudes and complications of pregnancy that differ for smokers and nonsmokers.