Elimination of fetal mice with sporadic malformations by spontaneous resorption in pregnancies of older females.

The frequency of offspring with sporadic spontaneous malformations in A/JKt mice was significantly smaller in litters from older mothers than in litters from younger mothers. Simultaneously the fetal resorption rate was significantly larger in the older group apparently accounted for most, if not all, of the reduced malformation rate in their surviving offspring. It therefore seems that the aged uterus and the abnormal fetus are involved in the process by which such offspring are eliminated.