Superovulation-induced intrauterine growth retardation in mice.

Existing animal models for inducing intrauterine growth retardation (IUGR) involve severe maternal compromise or acute fetal insult. We postulated that superovulation would produce IUGR gradually by enhancing fetal competition for nutrients. Mice were superovulated with pregnant mare serum and human chorionic gonadotrophin and killed on day 19 of gestation. Compared to controls, the mean number of fetuses was significantly increased; body, brain, liver, and placental weights were reduced; and brain/liver weight ratios were increased. Additional mice underwent partial unilateral oophorectomy before superovulation. Marked asymmetry in the number of fetuses in the two uterine horns of the same mother was produced, and the fetuses on the more crowded side manifested smaller brains and livers an increased brain/liver ratios. In the mouse, superovulation is a simple, preconceptual method for achieving IUGR and may be combined with partial unilateral oophorectomy to permit comparisons between fetuses with different growth characteristics within the same mother.