Sequence of implantation and fetal and placental weights in the rat

Rats (30) were injected intravenously with Evans blue dye on Day 5 of gestation and their uteri were examined to determine the position of early implantations. On Day 7 they were examined again for late implantations. Fetal sex and fetal and placental weights were determined at Day 22 (15 rats). The distribution of the 20% early implantations appeared random with respect to position in the uterine horn. There was no difference in fetal weight, placental weight or sex ratio between early and late implanting embryos.