Fetal death: comparative aspects in large domestic animals.

Anim Reprod Sci. 2004 Jul;82-83:415-30.
  
Fetal death: comparative aspects in large domestic animals.

Jonker FH.

Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht 
University, Yalelaan 7, The Netherlands.

Although the majority of pregnancy failures occur during the embryonic period, 
reports indicate that approximately 5% of detected pregnancies are lost during 
the fetal period, underlining the fact that fetal death is a substantial cause 
of economic loss. However, examination for fetal development or death during 
pregnancy is not performed routinely in domestic animals, and reference curves 
for normal fetal growth are, therefore, scarce. In this paper, the numerous 
possible causes of fetal death are reviewed briefly, with emphasis on the role 
of placental problems in fetal death and impaired fetal viability. In this respect, 
the role of placental insufficiency as a cause of pregnancy loss in twin 
pregnancies in monotocous species is well known, whereas the abnormal placental 
development leading to retarded fetal growth during pregnancies in recipients of 
in vitro produced (IVP) or nuclear transfer (NT) embryos has been less 
extensively documented. Fetal viability or death can be evaluated using hormonal, 
chemical and ultrasonographic parameters. For example, the viability of the 
feto-placental unit can be examined by measuring maternal plasma concentrations 
of oestrone sulphate or the placental proteins, including pregnancy-associated 
glycoprotein (PAG) and pregnancy-specific protein B-60 (PSPB-60). Low 
concentrations of any of these three indicate either no pregnancy, or if 
pregnancy was confirmed earlier, fetal death and abnormally high or low levels 
can indicate fetal abnormality. Ultrasound can be used to examine the fetal heart 
rate (FHR), the incidence of fetal movements (FM), the appearance of fetal fluids 
and the development of the fetus and placenta. However, although abnormal FHRs 
have been correlated to subsequent fetal death, it is important to remember that 
there is a large physiological variation in FHR at the end of gestation, due to 
different behavioural states and differences in FM patterns. Although monitoring
fetal viability and death using hormonal and ultrasonographic evaluations is possible
during pregnancy in domestic animals, there is considerable physiological
variations in the 'normal' values. Therefore, suitable combinations of tests 
need to be identified and more accurate reference values generated before such 
approaches can be considered reliable for monitoring the status of individual 
fetuses.

PMID: 15271470 [PubMed - in process]


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