Despite recent advances in neonatal care, ROP remains a great source of morbidity among the very low weight infant.  While immaturity and supplemental oxygen are already known major risk factors, ROP is a multifactorial disease process with many associated risk factors.  Our aim was to determine the association between hyperglycemia, GlyA and ROP and further compare them with other known risk factors. After multivariate logistic regression, hyperglycemia but not GlyA, remained a significant risk factor for ROP overpowering the other recognized risk factors.
Hyperglycemia is a common metabolic disturbance affecting up to 80% of very low birth infants. [2, 3] Hyperglycemia is known to be associated to oxidative stress and lead to increased resistance of vessel walls and changes in organ blood flow, thus exacerbating retinal hypoxia.  In an animal model of Neonatal Hyperglycemia-induced Retinopathy mimicking many aspects of retinopathy of prematurity, hyperglycemia inhibited retinal angiogenesis, induced apoptosis and retinal degeneration and led to inflammatory cytokine production. 
Garg et al, in a retrospective case–control study of 16 infants with BW < 1000 g and ROP Stage 3 or 4 were the first to associate increased glucose levels in the initial month of life to ROP.  Since then, 10 retrospective studies [5–7, 10–16] 1 prospective study  reported a significant association between hyperglycemia and ROP.
A subsequent meta-analysis, concluded that subjects with ROP had a significantly longer duration of hyperglycemia and an higher mean glucose level.  However, when combining the adjusted odds ratio, only a statistical trend was observed on duration of hyperglycemia with ROP.
Lee et al  in a retrospective study of 24 548 infants with hyperglycemia, (blood glucose > 180 mg/dL), concluded that hyperglycemia alone was not associated with severe ROP. However, blood glucose > 150 mg/dL and insulin use were associated with severe ROP. In our study, hyperglycemia was defined as blood glucose > 150 mg/dl but no infant needed insulin.
In 2019, a study by Jagla et al  reported that higher glycemic variability during the first week of life was associated with treatment requiring ROP. However, this association was lost on logistic regression. This loss might be due to real-time clinical intervention correcting the glucose level and limiting its consequences or due to the inability to detect differences due to relatively small sample size (n = 152). The same author assessed, the association between glycemic variability in the 1st week of life and type 1 ROP in a case-control study of 40 premature infants. After multiple regression, risk of type 1 ROP was only found to be associated with duration of oxygen exposure and higher glycemic variability. 
In our cohort, the median glycaemia was 95 mg/dl in infants with ROP and 85 mg/dl in those without, supporting that the difference in median glycaemia between these two groups is not large. Nevertheless, a trend for higher glycaemia does seem to exist in babies that develop ROP. Furthermore, and in line with the studies mentioned above, we also found that the presence of any event related to hyperglycemia was more frequent in infants diagnosed with ROP versus in those without (72,7% vs. 5.0%) even after multivariate analysis.
Due to the proposed association between hyperglycemia and ROP, the authors tried to uncover if GlyA’s values differed between infants with and without ROP and if so, if it would serve as clinical marker for ROP. Analogously to HbA1c, GlyA is one of the clinical markers for glycemic control and has been proven to be useful in the care of patients with neonatal diabetes mellitus. [18, 32, 33] Its main advantage over the widely used HbA1c, is that GlyA is not affected by hemoglobin’s metabolism or its variants.  Neonatal blood contains a high proportion of fetal hemoglobin (HbF). [20, 34] Additionally, preterm infants commonly undergo red blood cell transfusions which would also impair true evaluation of glycemic control with HbA1c. GlyA is not affected by the concentration of serum protein because it is expressed as a ratio to albumin, nor is affected by other proteins than albumin, and it has a high specificity as it reflects glycation products of a single protein. 
In the particular case of infants at risk for ROP, GlyA has the advantage of reflecting plasma glucose levels over a shorter period. Because the half-life of serum albumin (14d) is shorter than that of erythrocytes, it reflects the status of glycemic control changes for 2–4 weeks. [33 20] Moreover, GlyA reflects the fluctuation of plasma glucose as well as the mean plasma glucose,  thus having the potential of reflecting the glycemic control during the first phase of ROP.
Koga et al.  have previously studied the GlyA levels in the umbilical cord blood of 5 neonates at birth. Serum median GlyA level was 9.4 ± 1.1% (slightly lower than the lower limit of normal controls for adults). Suzuki et al.  tried to establish the reference intervals for GlyA in 58 healthy full-term newborn infants. Age-dependent reference values (95% CI) for GlyA in infants were between 4.9–9.4% at 4-7days, 5.5–10.1% 7–14 at 7-14days and 6.2–10.8% at 2-4weeks. In our cohort, the obtained median GlyA values in the 4 time points were similar to those reported by Suzuki et al. albeit with a greater range of values.
Because this was a proof of concept an interim analysis of GlyA was made halfway thru the study and it was found that GlyA alone was not a significant risk factor and therefore it was decided not to continue this analysis.
GlyA can be altered in patients with albumin metabolism disorders.  None of our infants had nephrotic syndrome, or altered thyroid function, however most of them received prenatal corticoids. Two studies have reported the effect of antenatally administered corticosteroids: one study did not show an effect on whole body amino acid metabolism , whereas in another, infants that received prenatal corticosteroids for lung maturation tended to have a 37% increase in albumin synthesis, although not statistically significant.  In our study there was no statistical difference in GlyA values between infants that received prenatal corticoids vs. those who did not.
Yudkoff et al reported that the relatively low serum albumin concentrations, typical of premature infants, appear to be referable to more rapid turnover of a small plasma pool rather than a diminution in the rate of albumin synthesis.  It is possible that the rapid turnover did not allow for sufficient glycation. Other possible reason for the lack of difference between GlyA in ROP and non-ROP infants might be due to the insufficient duration of hyperglycemia.
Both data from the Continuous Glucose Monitoring in Very Preterm Infants  and from 2 other similar studies [3, 30] monitoring the first week of life reported that the time spent in the predefined hyperglycemia was low (2.3–10.3% [3, 30, 38]). One hypothesis is that the occurrence rather than the duration of hyperglycemia might be associated with ROP.
Although not significant as a risk factor, with this study, we provide a reference range for GlyA at four different time points in premature infants that can be useful to assess the accurate glycemic status in these babies. Neonatal diabetes may affect gestational age and so a percentage of patients could present prematurely, or certain mutations may result in premature birth.  In a cohort of 750 patients with neonatal diabetes, 16% of patients with a genetic diagnosis were born prematurely. 
There are several limitations of our study, namely the small cohort, the use of ROP rather than treatment requiring ROP (due to limited sample size) and the inclusion of only two institutions from the same geographical area. We also recorded hyperglycemic events rather than its duration, due to the inability to continuously monitor the glucose level in the entire cohort.