Abstract
Placental weight is a valuable indicator of its function, predicting both pregnancy outcome
and lifelong health. Population-based centile charts of weight-for-gestational-age and parity
are useful for identifying extremes of placental weight but fail to consider maternal size. To
address this deficit, a multiple regression model was fitted to derive coefficients for predicting
normal placental weight using records from healthy pregnancies of nulliparous/multiparous
women of differing height and weight (n = 107,170 deliveries, 37-43 weeks gestation). The
difference between actual and predicted placental weight generated a z-score/individual centile
for the entire cohort including women with pregnancy complications (n = 121,591). The association
between maternal BMI and placental weight extremes defined by the new customised
versus population-based standard was investigated by logistic regression, as was the association
between low placental weight and pregnancy complications. Underweight women had a greater
risk of low placental weight [<10thcentile, OR 1.84 (95% CI 1.66, 2.05)] and obese women had
a greater risk of high placental weight [>90th centile, OR 1.98 (95% CI 1.88, 2.10)] using a
population standard. After customisation, the risk of high placental weight in obese/morbidly
obese women was attenuated [OR 1.17 (95% CI 1.09, 1.25)]/no longer significant, while their
risk of low placental weight was 59%-129% higher (P < 0.001). The customised placental weight
standard was more closely associated with stillbirth, hypertensive disease, placental abruption
and neonatal death than the population standard. Our customised placental weight standard
reveals higher risk of relative placental growth restriction leading to lower than expected birthweights
in obese women, and a stronger association between low placental weight and pregnancy
complications generally. Further, it provides an alternative tool for defining
placental weight extremes with implications for the placental programming of chronic disease.
Year
2020
Category
Refereed journal