The Maldevelopment of the Fetuses of Mice Treated with Gonadotropic Hormone before the Conception

Three groups of prepuberal, young adult and old mice in our colony originating from a Japanese mixed albino strain were injected once with 100 I.U. of mare gonadotropic hormone and soon after or a few days after injection were mated. In the former two groups, impregnation occurred immediately or some days or weeks after treatment. A tendency towards superfecundity and a high mortality of the fetuses were recognized in the mice of those groups, which conceived shortly after injection. Furthermore, the occasional occurrence of various skeletal malformations in the extremities, spinal column and palate were recognized in the fetuses of the treated prepuberal, and young adult mice. These anomalies were most often found in prepuberal cases. The length of the interval between the day of hormone injection and that of conception, seems to have no influence upon the frequency of malformations. As a mechanism for producing these malformations, effects of hormone, young maternal age and superfecundity were considered. When this hormone was given to old mice showing no oestrus cycle, pregnancy occurred in only one case, but the fetuses on it were found to be dead at midpregnancy.