Fetal Heart Rate in Relation to Body Mass

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Abstract
In contrast to the inverse relation of heart rate to body mass in adult mammals, the heart rate of immature fetuses is unrelated to body mass and approximately constant among different species. With maturation, fetal heart rate decreases in a large mammal but tends to increase in a small mammal. These maturational changes reduce the difference between the heart rate of a term fetus and the heart rate which is appropriate for body mass as calculated by means of the allometric equation for adults. Comparative physiology of fetal heart rate suggests that immature fetuses of small and large mammals have similar O2 consumption rates per unit body mass.