Effect of early maternal iron stores on placental weight and structure

Background Large placental size and low birthweight have been implicated as factors predicting high blood pressure in adulthood. Maternal anaemia has been suggested as a link. We investigated the interaction between maternal iron status and other factors known to influence birthweight and placental size. Methods In a prospective study of 1650 low-risk, singleton, caucasian pregnancies, we related placental size and birthweight to maternal iron status, socioeconomic status, and parity. Placental morphology was assessed in 17 randomly chosen primigravid pregnancies. Findings Parity was an important determinant of birthweight (mean standard deviation score −0·13 [SD 0·90] para 0; −0·24 [0·90] para 1; 0·32 [1·1] para 2; 0·21 [1·1] para ≥3; p < 0·0001) and placental weight (mean 655 g [SD 130]; 679 g [122]; 675 g [139]; 694 g [157], respectively; p=0·01). Cigarette smoking influenced birthweight only. Socioeconomic status had little effect after correction for parity. In addition to parity, the factors influencing placental weight were maternal height, weight, and serum ferritin concentration at booking, but not haemoglobin concentration. Serum ferritin concentrations were associated with folate intake and parity. In the placental morphology subset, serum ferritin concentration was inversely related to overall measures of peripheral villous capillarisation. Haemoglobin concentration showed no such association. Interpretation These findings show a relation between maternal anaemia and placental size and birthweight across the normal range for these measures. Low ferritin concentrations in early pregnancy were associated with increased placental vascularisation at term. The association between ferritin concentration and folate supplementation emphasises the importance of preconceptional health, particularly in women at high risk of iron deficiency.