Abstract
<title>Abstract</title> <p> Objective To evaluate changes in reticulocyte hemoglobin content (Ret‑He) and serum ferritin (SF) within the first 14 days after birth, and to explore the utility of Ret‑He alone or in combination with SF for assessing iron status in very preterm infants (VPI, gestational age < 32 weeks). We hypothesized that if iron‑restricted erythropoiesis were present, Ret‑He would decline in parallel with SF. Methods This retrospective study analyzed Ret‑He, SF, and complete blood counts obtained on postnatal day (PND) 3 ± 1 and PND 14 ± 1 in consecutive eligible VPIs. Because no clinically validated gold standard for iron deficiency exists in the first two weeks of life, we used an exploratory definition of low iron status as SF below the 10th percentile of the study cohort. This definition is not intended as a diagnostic threshold but to describe trends; it may introduce circularity when correlating with Ret‑He. No formal sample size calculation was performed due to the retrospective and exploratory nature; all eligible infants during the study period were included. Results A total of 145 VPIs were included. Mean (SD) gestational age was 30.1 (1.5) weeks, and mean birth weight was 1431.2 (301.2) g. Delayed cord clamping (DCC) was performed in 72 infants (49.7%) with a target duration of 30–60 seconds. Median (IQR) SF increased significantly from 178.50 µg/L (132.79, 233.43) on PND 3 to 220.00 µg/L (150.00, 274.61) on PND 14 ( <italic>P</italic> < 0.01). Ret‑He showed no significant difference: 28.80 pg (25.50, 30.25) on PND 3 vs. 28.70 pg (26.00, 30.10) on PND 14 ( <italic>P</italic> = 0.37). Subgroup analysis by gestational age showed that the pattern was consistent across gestational age subgroups, although formal statistical comparison was not performed due to the exploratory nature. In an exploratory analysis using the 10th percentile SF cutoff, Ret‑He showed limited ability to discriminate low from normal iron status (AUC 0.57 on PND 3 and 0.51 on PND 14). However, due to the circularity inherent in defining the condition by SF itself, these AUC values should not be interpreted as a true measure of Ret‑He’s diagnostic performance. Conclusion Our findings suggest that within the first 14 days after birth, endogenous iron stores are generally sufficient to support hematopoiesis, and routine iron supplementation before day 14 may not be necessary for all very preterm infants. SF on PND 14 was significantly higher than on PND 3, whereas Ret‑He remained stable. The pattern of iron status dynamics appeared consistent across gestational age subgroups, though formal statistical comparison was not performed. A Ret‑He value above 26.25 pg on PND 3 had a high negative predictive value in this exploratory analysis, suggesting it may help rule out functional iron deficiency, but prospective multi‑marker studies are needed to confirm this finding and determine the optimal timing of iron supplementation. </p>