Maternal Serum Ferritin Across Gestation and Risk of Small-for-Gestational-Age: A Longitudinal Cohort Study

Why It Matters

The study suggests that indiscriminate iron supplementation may increase SGA risk, prompting a reassessment of prenatal iron guidelines and emphasizing the need for trimester‑specific ferritin monitoring.

Key Takeaways

• Third‑trimester ferritin ≥18.1 ng/mL raises SGA odds 1.4‑fold.
• Risk climbs sharply above 12.1 ng/mL ferritin threshold.
• Persistent high ferritin (high‑high) doubles SGA risk.
• Dropping ferritin from high to medium eliminates excess SGA risk.
• Findings challenge routine iron supplementation for iron‑replete pregnancies.

Pulse Analysis

Iron deficiency remains a global public‑health priority, with the WHO targeting a 50% reduction in anemia among women of reproductive age by 2030. Consequently, iron supplementation has become a standard component of prenatal care in many countries. However, emerging data indicate that excess iron may be just as harmful as deficiency, contributing to oxidative stress and vascular dysfunction. This study adds a critical piece to the puzzle by quantifying the relationship between maternal serum ferritin—a proxy for iron stores—and fetal growth outcomes, highlighting a dose‑response curve that becomes detrimental beyond modest ferritin levels.

The researchers leveraged electronic health records from Shanghai First Maternity and Infant Hospital, measuring ferritin in early (8‑13 weeks) and late (29‑31 weeks) pregnancy. After adjusting for maternal age, BMI, parity and obstetric complications, they observed a 1.42‑fold increase in adjusted odds of SGA for women with third‑trimester ferritin ≥18.1 ng/mL. A spline analysis identified a risk inflection point at 12.1 ng/mL, suggesting that even modest elevations can impact placental nutrient transfer. Notably, women who maintained high ferritin across both trimesters or progressed from medium to high showed the strongest associations, whereas a reduction from high to medium normalized risk, underscoring the importance of dynamic iron monitoring.

Clinically, these findings argue for a shift from blanket iron prescriptions toward individualized strategies based on trimester‑specific ferritin thresholds. Obstetricians may consider routine ferritin testing in the first and third trimesters, reserving supplementation for those with genuine deficiency and avoiding excess in iron‑replete patients. Future prospective trials should explore optimal dosing regimens and investigate the mechanistic pathways—such as hepcidin dysregulation and ferroptosis—that link iron overload to impaired placental angiogenesis. Aligning supplementation practices with emerging evidence could reduce SGA incidence and improve long‑term child health outcomes.