Improvements to the mathematical description of prenatal growth

The exponential form of growth was used to describe prenatal growth in mouse, rat, guinea pig, swine, sheep, cattle and man. Instantaneous growth rate was permitted to vary as a function of time and, in litter bearing species, number of fetuses. Models for which instantaneous growth rate decreased linearly in time had a tendency to overestimate fetal weight from mid-gestation until midway through the last trimester of pregnancy and subsequently, underestimate fetal weight. When instantaneous growth rate varied as a quadratic function of time, a more accurate and precise prediction of fetal weights resulted.