Firstly, although a sufficient number of preterm-born children was included in order to obtain significant results for the primary outcome measures, this number was not adequate enough to reveal possible associations between plasma irisin levels and circulating EMPs and EPCs regarding preterm-birth-related maternal and/or neonatal morbidity, such as gestational hypertension and preeclampsia, BPD, IVH, ROP, etc. Including more neonatal units would have led to an increase in study participants and could further strengthen the results. This evidence concerns the gene FNDC5 and retinopathy of prematurity.