CD34 and retinopathy of prematurity: We found that infants who later developed ROP tended to have higher levels of circulating progenitor cells at birth than infants who did not, which was statistically significant for CD34+ (2.95[0.784–4.18]% vs. 0.746[0.10–3.99]%, P = 0.017), CD133+ (1.89[0.472–2.71]% vs. 0.548[0.072–2.39]%, P = 0.044), and CD34+CD133+ cells (1.65[0.443–2.40]% vs. 0.470[0.053–2.17]%, P = 0.029).