The role of ovarian steroids in placental development and endovascular trophoblast migration in the golden hamster.

Pregnant hamsters were ovariectomized on Day 7 and daily supplements of progesterone or progesterone plus oestradiol benzoate were given. Fetal development and survival was 14% and 62% respectively. Histological examination indicated that failure of labyrinthine development in the placenta resulted in failure to form an adequate number of maternal arterial spaces communicating with the base of the trophospongium to allow trophoblast migration in the related maternal spiral arteries. Progesterone was essential at all stages of gestation to sustain decidualized tissues and allow survival of a minority of fetuses. Oestradiol supplementation significantly increased fetal survival, but not to normal levels, suggesting that other oestrogens may be essential for the maintenance of normal hamster pregnancy.