Allometric metabolic scaling and fetal and placental weight

TL;DR

This study investigates how fetal and placental weights relate through allometric scaling, finding the relationship approximates a 3/4 power law and identifying factors influencing this relationship.

Contribution

It provides empirical evidence that the placental-birth weight relationship follows an allometric 3/4 power law and identifies key factors modifying this relationship.

Findings

The allometric exponent beta is approximately 0.78.

The relationship scales close to the predicted 0.75 power.

Multiple maternal and fetal factors significantly influence placental weight.

Abstract

We tested the hypothesis that the fetal-placental relationship scales allometrically and identified modifying factors. Among women delivering after 34 weeks but prior to 43 weeks gestation, 24,601 participants in the Collaborative Perinatal Project (CPP) had complete data for placental gross proportion measures, specifically, disk shape, larger and smaller disk diameters and thickness, and umbilical cord length. The allometric metabolic equation was solved for alpha and beta by rewriting PW= alpha(BW)^beta as Log (PW) = Log(alpha) + beta*Log(BW). Mean beta was 0.78+ 0.02 (range 0.66, 0.89), 104% of that predicted by a supply-limited fractal system (0.75). Gestational age, maternal age, maternal BMI, parity, smoking, socioeconomic status, infant sex, and changes in placental proportions each had independent and significant effects on alpha. Conclusions: In the CPP cohort, the placental - birth weight relationship scales to approximately 3/4 power.