Objective: Complete blood count (CBC) results should be interpreted by comparing them with reference ranges that vary according to gestational and postnatal age. This study aimed to establish normal reference values of CBC parameters for different gestational ages and birth-weights in the neona-tal population.

Material and Method: Complete blood count parameters obtained on the first day of life of neonates born between January 2015 and December 2019 were analyzed retrospectively. The distribution and correlation of hematological indices according to gestational age and birth-weight were examined.

Results: The mean gestational age of 340 newborns was 32.0±4.9 weeks and birth-weight was 1821.68±923.97 g. There was no difference between the two genders in terms of hematological indices, except that RDW value was higher in girls than in boys. There was a weak positive correlation between gestational age and leukocyte, platelet and erythrocyte counts (r =0.245, r =0.347 and r =0.310, respectively; p <0.05 in all comparisons). A moderate negative correlation was found between gestational age and MCV and MCH (r =-0.611, r =-0.564, respectively; p <0.05 in all comparisons). When hematological indices were compared according to gestational weeks, leukocyte and platelet counts were also different, similar to erythrocyte indices (p <0.05). When these hematological indices were analyzed according to birth-weight, similar results were obtained to those obtained accord-ing to gestational age.

Conclusion: The reference ranges for various hematologic indices in the neonatal period are not constant and change significantly with advancing gestational age. To identify abnormal results, normal reference values for CBC parameters must be determined for each neonatal population.