P1130049

1.3.4 Uterine pathology 1.3.4.1 Embryonic death

In the horse embryonic death occurs in 4 to 15% of all pregnancies between Days 10 and 50 (Chevalier and Palmer 1982, Simpson et al. 1982, Valon et al. 1982, Souires et al. 1988).

There are numerous ultrasonic signs that can be used to predict an impending embryonic mortality. In principle, all findings that indicate a deviation from the norma! should be interpreted as suspicious. Certain fea-tures are, however, morę characteristic and occur quite regularly.

An important feature indicating the viability of a conceptus is the anechoic naturę of the placental fluid. In the case of a resorption slight to moderate reflections will appear relatively soon within the fluid of the em-biyonic vesicle (Fig. 1.95). They are a sign of the in-creasing cellular content of the embryonic fluid and of the disorganization of the placental membranes.

The interface between the embryonic vesicle and its surrounding endometrium is smooth in the case of intact pregnancies. When this linę becomes wavy it may serve as an indication that an embryonic death is immi-nent (Fig. 1.96). Occasionally, the interface appears tor-tuous in which case the resorption will have already pro-gressed somewhat. The reason for this is the lack of in-ner tension in the vesicle which is caused by cessation of embiyonic fluid production and by its increased resorption. The endometrial folds are no longer stretched smooth by the conceptus , but rather protrude into it (Souires ct al. 1988).

In the case of a disrupted pregnancy the loss of the embryonic vesicle’s tension is associated with a loss of its typical shape. In the intact pregnancy the conceptus rc-mains strictly spherical untił Day 15 of gestation. If the embryonic vesicle assumes any other shape before this day it should be suspected to die. During later stages a change of shape can no longer be used as a reliablc in-dicator sińce physiological changes in shape occur sub-seąuently. In some cases of embryonic mortality a disor-ganization of the embryonic membranes have been ob-served (Fig. 1.97). Deviations from the typical arrangement of the allantoic yolk sac membranę occur in some cases of embryonic death during the ascending phase of the embryo (Ginther et al. 1985).

The lack of a heart beat is the most reliable sign for embryonic death. Shortly before death a bradycardia can be seen in some embryos. In the intact embryo the heart ratę is usually above 150 beats per minutę.

Another indication that an embryonic death might be in progress is the inadeąuate size of the vesiele (small-for-date) due to the subnormal volume of era-bryonic fluid (Ginther et al. 1985). An embryonic resorption occurring during the first 3 weeks of gestation usually runs a rapid course. It only takes a few days from noticing the first signs of a disorder until the embTyonic vesicle has disappeared. After the 3rd week some re-Sorptions run a protracted course (Fig. 1.96 and 1.97), ln mares that loose their embryo at a later stage, a pre-ceding subnormal vesicula.r size portends impending death, The involved embryonic structures sometimes continue to grow for several days and rareły for a few weeks (Darenius et al. 1988) yet do not obtain a norma! growth ratę and eventuaily die.