The effects of maternal cigarette smoking on placental morphology, histomorphometry, and biochemistry.

We related cigarette smoking during pregnancy to the macroscopic and microscopic morphology, histomorphometry, and biochemistry of the placenta among participants in The Prenatal Project, a randomized, controlled trial of nutritional supplementation during pregnancy. The aim was to ascertain if the harmful effects of cigarette smoking on the fetus were reflected, and possibly mediated, by changes in the placenta, and whether such changes might be modified by the nutritional supplements, parallel to the nutritional reversal of birthweight depression among heavy smokers. Maternal smoking was associated with increased alkaline ribonuclease (RNase) levels, possibly resulting in disturbed protein synthesis. More smokers had placentas with villous hyperplasia on histologic examination. This was accompanied by biochemical evidence of significantly increased cellularity (increased DNA/gm of placental mass and decreased protein/DNA ratios) and (nonsignificant) trends to reduced syncytial villous cell size on histomorphometry. There were joint effects of cigarette smoking and use of either form of nutritional supplementation on the fibrin and stoma components of the villi, but such changes are not necessarily pathologic. The significant reduction in pathology of the stem villi among smokers was confined to those who were nutritionally supplemented, particularly heavy smokers. This change may thus have reflected the protective effects of supplementation on the birthweight of the offspring of these heavy smokers.