The effect of smoking in pregnancy on early placental morphology.

Histomorphometric and ultrastructural investigations were performed on the placental tissue of 20 heavy smokers and 20 non-smokers. All pregnancies were artificially terminated at 9-14 weeks' gestation. When compared with values in non-smokers, smokers had significantly increased arithmetic and harmonic mean thicknesses (P less than .005 and P less than .05, respectively) of the villous membrane, and arithmetic and harmonic mean thicknesses (P less than .05 for both) of the trophoblastic layer. No significant difference was found between the groups for the mean number of capillary profiles per villous profile or for the mean volume fraction of the villi occupied by the trophoblast, the villous stroma, or the fetal capillary lumina. At the ultrastructural level, the mean number of areas presenting with syncytiotrophoblastic necrosis was significantly (P less than .001) higher in the smoking than in the non-smoking group, whereas no difference was observed for the mean number of areas demonstrating trophoblastic basal membrane thickening. These results suggest that smoking during the first months of pregnancy induces morphologic changes, which may explain biologic disturbances observed during early gestation and also later in pregnancy.