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 pregn ancies, we related placental size and birthweight to maternal iron status, socioeconomic status, and parity. Placental morphology was assessed in 17 r andomly 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] pa ra 2; 0.21 [1.1] para greater than or equal to 3; p<0.0001) and placental w eight (mean 655 g [SD 130]; 679 g [122]; 675 g [139]; 694 g [157], respecti vely; p=0.01). Cigarette smoking influenced birthweight only. Socioeconomic status had little effect after correction for parity. In addition to parit y, the factors influencing placental weight were maternal height, weight, a nd serum ferritin concentration at booking, but not haemoglobin concentrati on. Serum ferritin concentrations were associated with folate intake and pa rity. 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 increas ed placental vascularisation at term. The association between ferritin conc entration and folate supplementation emphasises the importance of preconcep tional health, particularly in women at high risk of iron deficiency.