Background: The World Health Organization recommends exclusively breastfeeding (EBF) for the
first 6 months of life. However, infants undergo WHO EBF for 6 months may have an increased risk of
anemia. Evidences regarding anemia associated with EBF are limited in the Northern part of Thailand.
Objective: To investigate the incidence of anemia at 6 months of age among EBF infants and non-EBF
infants, and risk factors of anemia at 6 months of age. Materials and Methods: The retrospective cohort
study was conducted in term-healthy infants at a well-baby clinic, Nakornping Hospital in 2019. Mothers
answered a questionnaire regarding history of breastfeeding. Hematocrit (Hct) level of infants was retrospectively
recorded at birth and 6 months of age. Infants with Hct less than 40% at birth were excluded.
Anemia was defined as Hct less than 33%. Data were analyzed comparing Hct between 2 groups of infants:
the EBF in the first 6 months of age and the non-EBF. Multivariable linear regression and exponential risk
regression were performed to investigate an effect of EBF. Results: Of 259 infants, 137 cases (52.9%) were
male, the overall incidence of anemia was 61 cases (23.6%). Prevalence of 6-month EBF infants was
45.9%. Incidence of anemia in the EBF and non-EBF infants was 24.4 and 22.9%, respectively. When
compared to the non-EBF group, no statistically significant differences were revealed, adjusted RR
0.98(0.61-1.58), p = 0.934. The mean of Hct in EBF and non-EBF infants were 34.18±3.23 and 34.57±3.38,
respectively. There was no statistically significant between mean of Hct of the two groups with adjusted
beta coefficient equals to -0.21(-1.09, 0.66), p = 0.631. Factors predicted anemia in infants at 6 months
of age included maternal age <20 years (adj. OR 3.88, 95%CI 2.68-5.60), >35 years (adj. OR 2.26, 95%CI
1.44-3.53), mothers with HbE positive (adj. OR 3.01, 95%CI 1.62-5.60). Conclusion: Overall incidence of
anemia in infants at 6 months of age was 23.6% classified as a moderate public health problem that
urgent investigation is needed. There was no statistical significance between incidence of anemia in the
EBF and non-EBF infants. EBF for the first 6 months of life does not increase the risk of anemia in healthy
infants compared with non-EBF.