Influence of conceptus number and weight on the amount of foetal fluid in the mouse.

The relation of extra-embryonic fluid weight to litter number and foetal and placental weight was studied in mice on the 18th day of pregnancy, in litters both of experimentally reduced and of normal number. Partial regression analysis showed that litter number and foetal weight both exerted a negative effect on fluid weight; placental weight had no significant effect. Increased foetal weight reduced weight locally; on the other hand the effect of litter number was exerted systemically, throughout both horns of the uterus.