Prenatal growth in Guinea-Pigs with special reference to environmental factors affecting weight at birth
Journal of Experimental Zoology Philadelphia 51: 51-91
Beginning with the 20-day stage, 410 fetuses have been removed at 5-day intervals from 113 guinea-plgs. The gestation period in these animals usually is 68 days. Weights were taken of the fetus, placenta, decidua basalis, fetal membranes, amniotic fluid, maternal uterus, and maternal body. The distance between placentas in unopened uteri was measured, and the orientation and sex of the fetuses was also determined. Where the uterus contained more than 3 fetuses, it was found that the growth of the fetuses was retarded after the 50-day stage. The placentas are probably affected first, and, because of their comparatively small size, reduce the amount of nutriment passed on to the fetuses. During the later stages of pregnancy, females carrying large, litters generally experience a decrease in body weight. No evidence of superfetation or super-fecundation could be found, but fetal resorption seems to be fairly common.