Objective: To compare the growth patterns of breast-fed (BF) and formula-fed (FF) infants with national growth references of Thai children and to determine whether the Thai growth references can be used to assess growth of BF infants who were fed according to Thai guidelines of infant feeding.
Design: Cohort study
Material and Method: One hundred and fifty six term infants (78 BF and 78 FF infants) were followed prospectively for 12 months. Milk was the only food source during the first 4 months and solid foods were introduced after 4 months of age. Body weight, length and head circumference were measured at the age of 1, 2, 4, 6, 9 and 12 months.
Results: Of the 156 infants, 140 completed the study (71 BF and 69 FF infants). BF and FF infants had similar mean weight and length from 0 to 6 months, thereafter BF infants had lower weight and length than FF infants with significant difference at 9-12 months in male infants and at 12 months in female infants (p < 0.05). Compared with national growth references of Thai children, mean weight and length of BF and FF infants in the study were significantly lower than the mean values of Thai infants from 0 to 1 months, thereafter mean weight and length of BF infants were close to the Thai references but those of FF infants were higher than the Thai references after 6 months with significant difference in weight from 9 to 12 months and length at 12 months. The incidence of malnutrition and obesity at 1 year of age was not different between the two feeding groups. Inadequate complementary food was the risk factor of infant malnutrition (adjusted RR 4.7, 95%CI 1.1-21.9, p 0.04).
Conclusion: BF and FF infants had similar weight and length from birth to 6 months, thereafter, FF infants had higher weight and length than BF infants and Thai growth references. Growth of BF infants correlated well with the national growth references of Thai children, so the Thai growth references can be used to assess growth of BF infants who were fed according to Thai guidelines of infant feeding.

Keywords: Breastfeeding, Formula feeding, Growth, Infant