Background: Previous studies of maternal risk factors for abnormal placental growth have focused on placental weight and placental ratio as measures of placental growth. We sought to identify maternal risk factors for placental weight and two neglected dimensions of placental growth: placental thickness and chorionic plate area.
Methods: We conducted an analysis of 24,135 mother-placenta pairs enrolled in the National Collaborative Perinatal Project, a prospective cohort study of pregnancy and child health. We defined growth restriction as < 10th percentile and hypertrophy as > 90th percentile for three placental growth dimensions: placental weight, placental thickness and chorionic plate area. We constructed parallel multinomial logistic regression analyses to identify (a) predictors of restricted growth (vs. normal) and (b) predictors of hypertrophic growth (vs. normal).
Results: Black race was associated with an increased likelihood of growth restriction for placental weight, thickness and chorionic plate area, but was associated with a reduced likelihood of hypertrophy for these three placental growth dimensions. We observed an increased likelihood of growth restriction for placental weight and chorionic plate area among mothers with hypertensive disease at 24 weeks or beyond. Anemia was associated with a reduced likelihood of growth restriction for placental weight and chorionic plate area. Pre-pregnancy BMI and pregnancy weight gain were associated with a reduced likelihood of growth restriction and an increased likelihood of hypertrophy for all three dimensions of placental growth.
Conclusion: Maternal risk factors are either associated with placental growth restriction or placental hypertrophy not both. Our findings suggest that the placenta may have compensatory responses to certain maternal risk factors suggesting different underlying biological mechanisms.