The placental weight ratio (PWR) is a common proxy for the balance between fetal and placental growth, and is defined as the placental weight over the birth weight. The objectives were (1a) to establish PWR distributions by gestational age for the overall population and (1b) for small, average and large for gestational age infants (SGA, AGA, LGA) and (2) to determine what pregnancy related conditions were associated with the PWR. The data were obtained using a hospital based retrospective cohort. Nonparametric quantile regression was used for the first and multinomial logistic regression for the second objective. The results show how the PWR changes across gestation. SGA infants had higher PWR’s than AGA and LGA infants. The multivariable analyses showed that the majority of risk factors were associated with a PWR\u3e90th percentile. The overall curves offer population standards, and the multivariable analysis suggests that the placental may have a particular compensatory response, each with a distinct pathophysiologic mechanism, but similar PWR outcome
