The Effect of Paternal Genotype on Parity-Dependent Changes in the Decidual Cell Reaction, Placental Weight and Fetal Weight in the Mouse

Summary. The extent of the decidual cell reaction on the 7th day of pregnancy in uniparous mice was found to be dependent on the reproductive history of the mother. It is postulated that these observations are due to differences in the mother's immunological status. Placental weight increased with parity but was unaffected by the sire of the first pregnancy. Fetal weight decreased with parity and there was some suggestion that the mother's immunological status may also affect fetal weight. There was also an apparent association between a reduction in decidual weight on the 7th day and a reduction of fetal weight on the 18th day of pregnancy.