The relationship between prenatal lethality or fetal weight and intrauterine position in rats exposed to diethylstilbestrol, zeranol, 3,4,3',4'-tetrachlorobiphenyl, or cadmium.

When administered orally during gestation, diethylstilbestrol (DES), zeranol (ZN), and 3,4,3',4'-tetrachlorobiphenyl (4CB) but not cadmium (Cd) exhibited significant developmental toxicity, including elevated embryo- and fetolethality and reduced fetal weight, in Sprague-Dawley rats. An analysis was performed to determine the effect of intrauterine position on these parameters. In control dams sacrificed after day 18, the general pattern was that fetuses at the ovarian end of the uterine horns were significantly lighter in weight, while the heavier fetuses were located in middle positions. Treatment with each of the chemicals reduced fetal weight equally across all uterine positions. An inverse of the weight pattern was observed for prenatal mortality in controls. Embryonic resorptions were relatively more frequent at both ovarian and cervical ends, while conceptuses at intermediate positions were less vulnerable. No significant alterations in this pattern were observed in treated litters. The frequency of late fetal deaths in 4CB-treated litters was significantly higher at the cervical end of the horn, however. No differences between horns or between sexes were observed in the relative position patterns for either weight or mortality.