Objective: Large placental weight and a high placental to birth weight ratio are both known predictors of higher adult blood pressure related to low maternal hemoglobin and a fall in mean cell volume. So we decided to study the association of maternal hemoglobin levels with placental weight, birth weight, and placental ratio.
Methods: This prospective study was performed on 500 pregnant women who were hospitalized in Amir- Almomenin Hospital in Semnan, Iran, for delivery from September 2001 to September 2002. Maternal hemoglobin concentration was measured at first trimester during prenatal care and before delivery using Coulter counter method. Birth and placental weights were measured at delivery. The patients with systemic disease, history of smoking, poly or oligohydramnious, placental abnormality, twin or multiple pregnancies, high blood pressure and fetal congenital anomaly were excluded from the study. Stepwise regression analysis was used to determine this association and p value<0.05 was significant.
 
Results: Krusskall Wallis and anova analysis showed that the lowest range of birth weight was associated with hemoglobin concentration of < 10 gr/dl in pregnancy (p=0. 1) and maternal age of less than 25 years old (p=0.007). The maximum of placental weight was in pregnant women with parity of 3 to 4 (p=0.005). The maximum of placental ratio (placental weight / birth weight) was with hemoglobin concentration of 9-9.9 gr/dl in third trimester. (p=0.001)
 
Conclusion: Using multiple regression analysis, we detected a positive correlation between birth weight and late maternal hemoglobin levels (p=0.0179), between placental weight and parity (p=0.0008) and a negative association of placental ratio with maternal hemoglobin concentration in first trimester (p=0.0034).