# Changes in Fetal Hemoglobin in Very Preterm Infants Born Small for Gestational Age: A Retrospective Observational Study

## TL;DR

This study found that fetal hemoglobin levels decrease similarly in very preterm infants born small or of normal size, with blood transfusions affecting only the latter group.

## Contribution

The study provides new insights into how fetal hemoglobin changes in very preterm infants based on birth size and transfusion history.

## Key findings

- HbF fractions decreased similarly in SGA and AGA very preterm infants over time.
- RBC transfusions reduced HbF in AGA infants but not in SGA infants.
- Fetal hypoxia may explain stable HbF levels in SGA infants.

## Abstract

Background: Small-for-gestational-age (SGA) preterm infants are at higher risk for oxidative stress-related complications than appropriate-for-gestational-age (AGA) preterm infants. It has been proposed that HbF may be higher in SGA than in AGA infants due to fetal hypoxia. Aim: The aim of this study was to compare postnatal changes in HbF fractions in very preterm SGA and AGA infants and in subgroups of these patients who had been transfused with red blood cells (RBCs) or not. Methods: We studied 30 SGA and 60 AGA very preterm infants with a gestational age of 27.7 ± 1.6 and 27.9 ± 0.7 weeks, respectively. HbF fractions were recorded daily during the first week of life, at 14 ± 2, 21 ± 2, and 28 ± 2 days of life, and 36 weeks (±3 days of life) of postmenstrual age. Results: The HbF fractions measured from the first day of life to the 36th week of postmenstrual age decreased significantly in both the groups, without differences between the groups. Transfused and non-transfused SGA infants had similar values of HbF fraction, while transfused AGA infants had lower values of HbF fraction than non-transfused infants. Conclusions: HbF fraction decreased similarly in the postnatal period in very preterm SGA and AGA infants. RBC transfusions did not affect hemoglobin fraction (HbF) values in SGA infants but were associated with a reduction in HbF in AGA infants. These findings may be due to the effect of fetal preconditioning hypoxia in very preterm SGA infants.