Chorionic surface area in conceptuses from sows treated with progesterone and oestrogen during early pregnancy

Treatment of sows with 25 mg progesterone and 12.5 microgram oestrone daily between 14 and 23 days of gestation resulted in an increase of 15% of chorionic surface area and an increase in volume of allantoic fluid when examined at 30-35 days of gestation. In contrast, there were no significant differences in chorionic surface area or allantoic fluid volume between treated and control sows examined at 46-50 days of gestation. This suggests that progesterone-oestrone treatment of the sows during early pregnancy has only a short-lived effect on development of the allantochorion.