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Conceptus (placental membranes, fetal fluids and fetus) development in intact control (IC) and unilaterally hysterectomized-ovariecto-mized (UHOX) gilts was characterized between days 20 and 100 of gestation to evaluate the effects of intra-uterine crowding in UHOX gilts having essentially the same number of potential embryos, but only one-half the endometrial surface area of IC gilts. Results indicated that die number of live and dead embryos, percent fetal survival, fetal crown-rump length and fetal weight were not significantly (P<.10) different prior to day 35 of gestation in IC and UHOX gilts; however, all placental measurements were significantly (P<.01) greater in IC gilts at all stages of gestation. The data suggest that placental insufficiency was the primary cause of increased fetal death and decreased fetal growth which occurred after day 35 of gestation in UHOX gilts. Fetal growth was significantly (P<.01) correlated with placental development. Progestins, estrone and estradiol concentrations in plasma from the radial vein, uterine vein, uterine artery and allantoic fluid and amniotic fluid were characterized. A rapid increase in allantoic fluid estrone and estradiol concentrations between days 20 and 30 of gestation was temporally associated with a concurrent increase in allanotic fluid volume. This early increase in allantoic fluid volume may cause expansion of the chorio-allantoic membranes, forcing these membranes into apposition with the uterine endometrium, and affect the extensiveness of the placental surface area established. It is suggested that the extent to which placental development occurs between days 20 and 30 of gestation has a significant influence on subsequent fetal growth and survival.
Knight et al. (Fri,) studied this question.