Correlation of Placental Anthropometric Measures in Subsequent Pregnancies: The National Collaborative Perinatal Project

Background: Previous studies demonstrate a high correlation of birth weight among siblings. Several studies have shown that gross placental anthropometric measures are associated with birth weight, however little is known about the correlation of placental anthropometric measures (placental weight, placental thickness, largest diameter and smallest diameter, chorionic plate area) in subsequent pregnancies.  Moreover, little is known about the influence of gender concordance on the correlation of placental anthropometric measures.

Methods: We conducted an analysis of 1854 mothers enrolled in the National Collaborative Perinatal Project, a prospective cohort study of pregnancy and child health.  We evaluated the correlation between gross placental anthropometric measures in the first and second pregnancies of the analytic sample.  In addition, we examined the correlation among gender concordant and gender discordant pregnancies. 

Results: Placental weight, largest diameter, smallest diameter, chorionic plate area and placental thickness in the first pregnancy were significantly correlated with that of the subsequent pregnancy with correlation co-efficients 0.39, 0.31, 0.27, 0.34 and 0.24 respectively (all p<0.05).  Placental thickness was significantly higher in the second pregnancy compared to the first pregnancy (22.2±4.8 vs. 21.9±4.9 mm, p=0.04), however there were no significant differences in placental weight, chorionic plate area, largest diameter and smallest diameter.  We found no significant associations between gender concordance and correlations between placental measures in the first and second pregnancies. 

Conclusion: Moderate correlations exist between gross placental measures between first and second pregnancies. Gender discordance was not a significant influential factor on the correlation of placental measures between first and second pregnancies.