A thoroughbred mare aborted an 8-month old autolysed foetus as shown:
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What abnormalities are evident on external examination?
The amniotic part of the umbilical cord is very long and very twisted. The twisting has caused obstruction of the thin-walled urachus within the cord and the formation of a large urachal dilatation.
The fetal abdomen is distended (with an excess of peritoneal fluid).
Fetal tissues are autolysed.
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Which of these is likely to have contributed directly to foetal death, and what is the likely pathogenesis?
The twisting in the umbilical blood vessels caused increased resistance to blood flow in both directions and the resulting poor placental perfusion will have lead directly to fetal death. *Histological examination of the peripheral regions of the allantochorion showed microthrombi in stromal vessels, and necrosis and calcification in many villus cores. Small- to moderate-sized urachal dilatations associated with twisting are often noted as incidental findings in both normal and aborted fetuses and are not life-threatening.
The dilated abdomen is a secondary feature resulting from serosal effusion (not to be confused with the same change in EHV-l abortions).
At the time of abortion, histologically the outer villus epithelium often appears relatively well preserved, probably as a result of direct diffusion of nutrients and oxygen across the fetomaternal junction. This may in part account for why placental dehiscence and expulsion of the fetus in this type of abortion occurs some time after fetal , the fetus characteristically being very autolysed when aborted.
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How important are these changes as a cause of abortion?
Fetal death associated with excessive cord length (over 80 cm total length and 41 cm amniotic length), twisting and vascular compromise is currently the commonest single cause of observed non-infectious abortion.
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What used to be the commonest cause of abortion in thoroughbreds?
Before ultrasound scanners became routinely used in pregnancy diagnosis, twinning was the commonest cause of abortion in Thoroughbreds.
