Effects of cigarette smoke exposure on early stage embryos in the rat

It is well recognized that cigarette smoking in pregnant women exerts many deleterious effects on their progenies; intrauterine growth retardation, and increases in perinatal mortality and premature births. The fetal growth retardation also has been reported in animals exposed to cigarette smoke. The authors previously demonstrated that cigarette smoke exposure in pregnant rats retarded the growth of fetuses from mid to late stages of pregnancy. In addition, the weight of uteri containing embryos in animals inhaling the smoke was smaller, although not significant, than that in the control on day 7 of pregnancy. Based on these findings, it was suggested that the growth of embryos in early stage seemed to be harmfully affected as well as during mid and late stages of pregnancy. However, since the uterine weight in early pregnancy was measured in the previous study instead of the direct observation of early stage embryos, it remained unclear whether the early development of embryos was really influenced by cigarette smoke exposure or not. The present study was designed to observe the effects of cigarette smoke inhalation by pregnant rats on early development of embryos from fertilization to implantation.