Stereologic examination of placentas from mothers who smoke during pregnancy.

Objective: Structural changes in the placenta might contribute to the lower birth weight seen among infants born to mothers who smoke cigarettes. In this study, a morphologic examination and a stereologic quantitation of placentas from mothers who smoked cigarettes and who did not smoke cigarettes during pregnancy were performed.

Study Design: Twenty-five placentas from mothers who did not smoke cigarettes, 15 placentas from mothers who smoked 5 to 10 cigarettes per day, 16 placentas from mothers who smoked 11 to 20 cigarettes per day, and 16 placentas from mothers who smoked >20 cigarettes per day were delivered at term after normal pregnancies and were fixed by dual perfusion. The volume and the surface area of villi, the trophoblast volume, and the volume and the surface area and length of villous capillaries were estimated. A measurement of the concentration of cadmium in serum was used to assess the validity of information concerning smoking habits.

Results: No differences were shown in the total volume of placenta between the groups. The estimated volume and surface area and the calculated lengths for villous capillaries were significantly reduced in all 3 groups of smokers. A significant increase of the trophoblast volume was observed in the mothers who smoked cigarettes.

Conclusion: Cigarette smoking during pregnancy influences the placental vasculature. The reduced dimensions of fetal capillaries in villi may affect the placental blood flow, and the diminished area for exchange of gases and nutrients between the mother and the fetus will increase the risk of fetal undernourishment.