According to the findings of a randomized clinical trial (part of ECLIPSES Study), tailoring iron supplementation to initial hemoglobin (Hb) levels in non-anemic pregnant women supports favorable fetal development within each stratum, yet excessive doses detrimentally impact optimal growth. Specifically, high prenatal iron doses within each stratum elevate the risk of deviating from "optimal" fetal and birth parameters, underscoring the importance of personalized supplementation protocols based on Hb levels to optimize fetal growth outcomes.

Researchers examined the impact of prenatal iron use tailored to pregnant women's initial Hb levels on fetal and neonatal growth parameters until delivery in those residing along the Mediterranean coast of northern Spain. A total of 791 volunteers participated, all of whom received iron supplementation during pregnancy based on their Hb levels at the 12th week of gestation. Those in stratum 1 (Hb: 110-130 g/L) were administered either 40 or 80 mg of iron daily, while those in stratum 2 (Hb > 130 g/L) were given either 40 or 20 mg of iron daily.

Fetal biometric and anthropometric estimations were examined in each trimester and at birth, respectively. In stratum 1, employing 80 mg/day instead of 40 mg/day magnified the likelihood of fetal head circumference exceeding the 90th percentile (Odds ratio [OR] = 2.49, p = 0.015) in the second trimester, as well as fetal weight (OR = 2.36, p = 0.011) and femur length (OR = 2.50, p = 0.018) falling below the 10th percentile in the third trimester. In stratum 2, employing 40 mg/day instead of 20 mg/day elevated the risk of fetal head circumference surpassing the 90th percentile (OR = 3.19, p = 0.039) in the third trimester.

Furthermore, a greater likelihood of delivering a large-for-gestational-age (LGA) baby (OR = 2.35, p = 0.015) in terms of birth weight was witnessed among women in stratum 1 receiving 80 mg/day. It is imperative to tailor prenatal iron supplementation to the individual needs of each pregnant woman, specifically tailored to their initial Hb levels, to ensure optimal fetal development, as excessive doses of iron seem to negatively affect fetal growth.