Objective: To characterize neonatal iron stores depending on gestational age (GA) at term.
Study design: Participants were 751 mother-newborn pairs from the placebo arm of a randomized clinical trial of prenatal iron-folate supplementation in China. We compared mean cord serum ferritin (SF) by weeks GA and, following the general linear model, assessed whether maternal iron deficiency (ID) influenced relations between GA and cord SF.
Results: Controlling for covariates, cord SF increased between 37 and 41 weeks (ps < 0.05-0.01). Cord SF was lower in infants of ID vs. non-ID mothers (geometric mean 96.3 [95% CI: 91.3-101.6] µg/L vs. 115.9 [95% CI: 105.0-127.8] µg/L, effect size = 0.33 SD, p = 0.0012). There was no significant increase with GA among infants of ID mothers. For non-ID mothers, cord-blood SF increased sharply with GA until 38 5/7 weeks, after which it plateaued.
Conclusions: The findings emphasize that neonates at 37-38 weeks, although considered term, are not fully mature.