Ultrasonography: embryonic death
Keywords: ultrasound, equine, embryonic death, EED
The majority of embryos are lost even before they are detectable by ultrasonography. In those cases, animals never recognize pregnancy and return to estrus. In mares, embryonic death is usually seen on ultrasonography during routine pregnancy diagnosis. Ultrasound examinations should occur several times during early gestation, the rationale for each examination being specific at each stage. Those stages and the rationale for those examinations are beyond the scope of this entry. Familiarity with the appearance of embryos at each of these examination is essential for recognizing signs of early embryonic death.
In the composite image below, the top inset shows the hyper-echogenic remnants of a degenerating 14 day old embryo. The lower image shows complete absence of the embryo, amnion and allantois; normally obvious of that stage of pregnancy. The fetoplacental unit is also collapsing, a sign of embryonic death.
Image size: 1000 x 750px
The next image shows a 55 day pregnancy. On transrectal palpation it resembled a 35 to 38 day pregnancy; smaller than expected. Uterine tone was still present but this is common in cases of embryonic death after the recognition of pregnancy. Fragmentation of embryonic membranes and the collapse of the embryonic unit typify its recent or impending death. The lower arrow shows the degenerating embryo and the amnion, the upper arrow shows collapse of the entire embryonic unit. Collapse of the embryonic unit is probably due to failure of the sodium pump within the fetal membranes with a consequent inability to retain water in the trophoblast.
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A high resolution image (below) showing a fetus that was normal at 45 days of gestation. At 60 days, the fetus had died and together with its placenta, was in a advanced state of degeneration. Judging by the size of the fetal-placental unit, it had died several days before the 60 day pregnancy diagnosis and a substantial amount of fetal fluid had already been lost. Several days later, the uterus was devoid of any fetal remnant and appeared to be normal.
Image size: 571 x 580 px Author and holder of copyright: Dr A. King. Millbrook Equine Veterinary Clinic. Millbrook, NY 12545
Note: Loss of pregnancy from 55 day, suggests endometrial incompetence as a result of endometrial fibrosis. That is because the yolk sac has been depleted by 55 to 60 days and the fetus has become completely reliant on the endometrium for its sustenance. Abortion ensues. Endometrial biopsy is usually suggested before re-breeding is attempted.
