Objective: Iron deficiency anemia is a very common health problem during pregnancy and intravenous (IV) iron substitution has become part of routine management. However, recent studies have raised concerns about the association of IV iron infusion and the development of secondary transitory hypophosphatemia (HP) in adults, including pregnant women. We aimed to evaluate the impact of IV iron administration during pregnancy on the phosphocalcic metabolism of newborns.

Methods: A prospective, single-center, observational study was performed from December 2022 to May 2023 at the maternity facility of Geneva University Hospitals. We included women treated with either IV or oral iron during pregnancy. At delivery, a maternal blood sample was collected to assess hemoglobin, hematocrit, and levels of ferritin, phosphate and calcium, as well as an umbilical cord blood sample to assess levels of phosphate and calcium. Univariate and multivariate analyses were performed to evaluate the contribution of IV iron substitution on cord blood phosphatemia and calcemia, considering potential confounding factors. Neonatal HP was defined as a phosphate level <1.3 mmol/L.

Results: Forty-three pregnant women were included in our study. Among these, 22 were treated with ferric carboxymaltose and 21 with oral iron. There were three cases of maternal HP in the IV iron group (13.6%) and one (4.8%) in the control group (p value for the difference= .607). We observed one case (4.5%) of neonatal HP in the IV iron group and no cases in the control group. Median cord blood phosphatemia and calcemia were 1.7 mmol/L vs. 1.71 mmol/L and 2.67 mmol/L vs. 2.64 mmol/L in the IV iron and oral groups, respectively. After adjustment, IV iron administration had no impact on cord blood phosphate (p= .919) and calcium (p= .891) levels.

Conclusion: No impact of IV iron administration during pregnancy was observed on the newborn phosphocalcic metabolism.