A quantitative study on the effects of maternal smoking on placental morphology and cadmium concentration

The aim of this study was to quantify the effects of maternal cigarette smo king on placental morphology, paying particular attention to variables know n to be influential in facilitating oxygen diffusion. Structural quantities were estimated by stereological analyses of placental samples drawn from n on-smoking and smoking women whose smoking habits were assessed both subjec tively (from volunteered cigarette consumption) and objectively (by determi ning levels of plasma cotinine, a major metabolite of nicotine). Concentrat ions of placental cadmium were also measured. In the smoking group, materna l and fetal haematocrits were elevated and mean birthweight was reduced. Wi thin placentae, the most significant alterations were increases in cadmium levels, the relative volumes of maternal intervillous space, the relative s urface areas of fetal capillaries and decreases in the relative and absolut e volumes of fetal capillaries. Findings indicate that changes in capillary volume are the result of a decrease in mean capillary diameter rather than total length. The mean thickness of the trophoblast component of the villo us membrane was also increased in the smoking group. Although increased hae matocrits suggest that fetuses of smoking mothers suffer hypoxic stress, th ese morphological changes are likely to compromise, rather than assist, tra nsplacental oxygen transfer. This is in marked contrast to the adaptive cha nges seen in pregnancies associated with preplacental hypoxia and suggests that other factors might be compromising the fetoplacental unit. Finally, a lthough the morphological changes associated with maternal smoking seem to be the result of an all-or-none, rather than dose-dependent, effect, the av ailable evidence is nor conclusive. (C) 2000 Harcourt Publishers Ltd.