Composition of the fetal and maternal guinea pig throughout gestation.

The guinea pig is a small animal species in which the conceptus constitutes a large proportion of maternal weight at term, thereby imposing a major metabolic demand on the mother during pregnancy. In addition the neonatal fat concentration is similar to the human making the guinea pig an interesting model for comparative physiologic study. The purpose of our study was to describe the fetal and maternal physical/chemical growth characteristics of the Hartley albino guinea pig throughout the latter half of gestation. Forty-eight pregnant adult and 122 fetal guinea pigs were sacrificed at intervals throughout gestation and the carcasses analyzed for a variety of growth parameters. The fetal growth rate during the last 8 days of gestation (5.8 g/day) was 9.7 times faster than from 30 to 40 days of gestation (0.6 g/day). The fetal mass comprised 55.4% of the maternal weight gain at term. Fetal energy increased from 403 cal/g at 30 days to 1950 cal/g at term and was paralleled by an increase in fetal fat concentration from 0.3 to 9.8% (wet weight). Nitrogen concentration increased from 0.9% wet weight at 30 days to 2.6% at term. An increasing carbon concentration and carbon:nitrogen ratio was also evident. Fetal water concentration declined from 91.6 to 67.8% during latter gestation. On a wet weight basis, the concentration of fetal sodium remained stable throughout the latter half of pregnancy; potassium, magnesium, iron, calcium, and phosphorus concentrations increased. In contrast to the changes in fetal composition, maternal energy, fat, protein, water, sodium, potassium, calcium, phosphorus, magnesium, and iron concentrations remained relatively constant throughout pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)