Metabolic scaling law for mouse fetal and placental weight

Human birth weight does not scale linearly with the weight of the placenta: placental mass (PM) is proportional to the fetal mass (FM) raised to the scaling exponent of 0.75 (PM ∼ FM(0.75)) [1,2]. The mouse is a common model for studying genetic and physiological backgrounds of placental development, function and pathologies. However, to date it has not been known how placental weight scales relative to embryo weight in mice. We analyzed E12.5 litters of CD1 wild-type mice, and found that the mouse placental weight demonstrates a power-law scaling relationship with fetal weight; the value of the scaling exponent is approximately 0.72.