Visceral fetal examinations

Visceral Fetal Examinations. The examination of the abdominal and thoracic viscera of fetuses is performed either fresh without fixation ( Staples technique ) or after Bouin s fixation by making freehand razor blade sections ( Wilson s technique Wilson, 1965). Both techniques have advantages. The fresh examination technique, which may require less training for thorough proficiency, provides a more easily interpreted view of heart anomalies. The examination must be performed on the day the dam is terminated, however, so having a large number of litters to examine in one day requires that a large team of workers be committed to the task. 

The fetuses are then examined. Full details of fetal examination are provided in other chapters of this book some techniques are performed on fresh fetuses, while other techniques require prior fixation of the fetuses. For rodents, one half of the fetuses in each litter should be examined for soft tissue (visceral) changes the remainder should be examined for skeletal changes. Rabbit fetuses should be examined for both soft tissue and skeletal abnormalities the heads from half of the fetuses should be examined by serial sectioning, with skeletal examination conducted on the remainder of the fetus. 

Key words Fetal examination, Visceral, Fresh soft tissue. Fixed tissue. Microdissection... 

Exposure of pregnant Alderley-Park rats to 1,4-dichlorobenzene via inhalation at levels up to 508 ppm for 6 hours per day on Gd 6-15 did not result in developmental effects in the offspring (Hodge et al. 1977). End points examined included the number of viable fetuses, fetal weight, litter weight, sex ratio, external abnormalities, and skeletal and visceral abnormalities. 

Each fetus is examined for external defects. After evisceration of approximately one half of each litter, the eviscerated fetal carcasses are fixed and processed for skeletal examination (see Chapters 16 and 17). The remaining fetuses are preserved for fixed visceral examination (see Chapters 19 and 20). 

Both the fresh and fixed visceral examinations are destructive nonetheless, a trained fetal morphologist can at least reexamine the retained fixed organs and tissues. This is particularly of value for rodent specimens. Photographs of abnormalities can also be taken (see Note 2). 

Viable fetuses should be labelled for identification, examined for visible malformations, visceral and skeletal anomalies and variations, sexed and weighed. Since there is an inverse correlation between number of fetuses per litter and individual fetal weight, total litter weight is also a useful measurement. 

Viable fetuses are examined for external, visceral, and skeletal malformations and variations, and the sex is determined. Individual fetal weight and identification allow external, visceral or skeletal findings to be linked to individual weights. Because there is a correlation between the number of fetuses in a litter and fetal weight, fetal weight can be analyzed with litter size as a covariate. 

In contrast to primates, which abort dead embryos, dead rodent embryos are resorbed and the implantation site is recorded as a resorption site. The numbers of living and dead fetuses, and the number of resorption sites, are counted, and fetal weight, sex, and external malformations are recorded. Fetuses can either be inspected fresh in evaluation of internal soft tissues (known as the Staples technique) or can be placed in a fixative (usually Bouin s solution) and sectioned at a later time (Wilson technique). Other fetuses are fixed in ethanol, cleared in potassium hydroxide, and the cartilage and bone are stained with Alcian Blue and Alizarin Red, respectively. The US FDA recommends that one-third of the rodent fetuses be subjected to visceral examination and that two-thirds be studied for abnormalities of cartilage and bone. The US Environmental Protection Agency (EPA) recommends that one-third to one-half of each litter be examined for skeletal anomalies. For rabbits, all fetuses are to be examined for both visceral and skeletal malformations. 

Several studies have examined the safety of cow s foot in pregnant diabetic and healthy rats using an orally administered aqueous extract at doses of 500 mg/kg on gestational days (GD) 0 to 4, 600 mg/kg on GD 5 to 14, and 1000 mg/ kg on GD 15 to 20. No teratogenic activity and no effects on maternal weight gain, reproductive performance, or fetal or placental development were observed. Treatment with cow s foot reduced the number of skeletal abnormalities and visceral malformations observed in offspring of... 

Goldman et al. (1988) administered VX subcutaneously to Sprague-Dawley rats on d 6-15 of gestation at 0, 0.25, 1.0, or 4.0 Xg kg d . Body weight, frequency of visceral and skeletal abnormalities, litter size, and sex ratios were evaluated. The examined fetuses showed no evidence of malformations. Fetal body weight, litter size, and sex ratio were within normal limits. Blood ChE activity levels were not monitored. 

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