Iron deficiency anemia (IDA) is a very common health problem during pregnancy and intravenous (IV) iron substitution has become part of routine management. Recent studies have raised concerns about association of IV iron infusion and development of secondary transitory hypophosphatemia (HP) in adults including pregnant women. The study aimed to evaluate the impact of IV iron administration during pregnancy on newborn's phosphatemia.

The investigators conducted a prospective, single-center, observational study in the Geneva University Hospitals (HUG), from September 2022 to March 2023. Pregnant women treated either with IV iron or with oral iron during pregnancy were included. At delivery, a maternal blood sample to assess hemoglobin, hematocrit, ferritin, phosphate and calcium and an umbilical cord blood sample to assess levels of phosphate and calcium were collected. Difference in demographics and clinical characteristics between the two groups were explored using univariate analyses. Multivariate analyses were performed to test the contribution of IV iron substitution on cord blood phosphatemia and calcemia, considering potential confounding factors. Neonatal HP was defined as a phosphate level lower than 1.3 mmol/L.

Inclusion Criteria:

• Single pregnancy
• Term (>37SA) pregnancy
• Oral or IV iron substitution from second trimester

Exclusion Criteria:

• Multiple pregnancy
• Fetal anomalies
• Preterm birth

Women with an uncomplicated term (≥ 37 weeks) single pregnancy who received IV iron or oral iron substitution from the 2nd trimester of pregnancy (>12 weeks of pregnancy) to the day of delivery