PROSPECTIVE COHORT STUDY OF FACTORS INFLUENCING THE RELATIVE WEIGHTS OF THE PLACENTA AND THE NEWBORN-INFANT

Objectives: To determine the demographic, environmental, and medical f actors that influence the relative weights of the newborn infant and t he placenta and compare this ratio with other factors known to predisp ose to adult ill health.Design: Prospective cohort study. Setting: The tertiary referral centre for perinatal care in Perth, Western Austral ia. Subjects: 2507 pregnant women who delivered a single live infant a t term. Main outcome measures: Placental weight, birth weight, and the ratio of placental weight to birth weight. Results: By multiple regre ssion analysis the placental weight to birthweight ratio was significa ntly and positively associated with gestational age, female sex, Asian parentage, increasing maternal body mass index, increased maternal we ight at booking, lower socioeconomic status, maternal anaemia, and inc reasing number of cigarettes smoked daily. There were no consistent re lations between the placental weight to birthweight ratio and measures of newborn size. Conclusions: The ratio of placental weight to birth weight is not an accurate marker of fetal growth. In its role as a pre dictor of adult disease the ratio may be acting as a surrogate for oth er factors which are already known to influence health and may act bef ore or after birth. Determining the role that relative growth rates of the fetus and placenta have in predisposing to adult disease requires prospective study to account for the many confounding variables which complicate this hypothesis.