The uterus and pregnancy failure

The equine embryo endures a long oviducal transport time and does not enter the uterus until 6–6.5 days after ovulation where it requires an hospitable environment to survive and develop normally. However, in some instances, the uterine environment may not be conducive to embryonic survival and the embryo may be powerless to swing things in its favour. The steroid hormones, progesterone and oestrogen, orchestrate conditions in the pregnant uterus and by Day 40 the placental gonadotrophin, equine chorionic gonadotrophin (eCG), also begins to play a part in this process. This presentation will focus on the hormonal aspects of the interactions between the equine conceptus and the uterus and it will examine shortcomings in these relationships which might lead to pregnancy failure.
On arrival in the uterus one of the embryo’s first jobs is to signal its presence to the mother to prevent her releasing luteolytic pulses of prostaglandin F2α from the endometrium and so prolong the functional life of the corpus luteum (CL). If this maternal recognition of pregnancy signal succeeds the uterus will remain dominated by progesterone for the remainder of gestation, secreted first by the prolonged primary CL, then by a variable number of accessory CL and, finally, from the placenta. Hence, the traditional view is that, throughout pregnancy, the uterus remains a progesterone-dominated environment.  […]