Objective: To determine the incidence and risk factors of iron deficiency (ID) among preterm infants when they reached four months postnatal age.

Materials and Methods: The present study was a prospective cohort study. Infants born at 34 weeks’ gestation or earlier, weighing 2,000 grams or less, and treated at a university hospital in Bangkok, Thailand between January 2010 and June 2014 were enrolled. Study data collected included demographic and clinical information during hospitalization, breast milk or formula, and iron supplementation reported during follow-up visits, and studies of iron status at 4-months postnatal age. Univariate and multivariate analyses were performed to identify factors associated with ID.

Results: One hundred twenty-one infants completed the four months follow-up. At hospital discharge, all infants were exclusively or partially breastfed. Prophylactic ferrous sulfate was prescribed in 110 infants. At 4-month, 65% were exclusively or partially breastfed. Incidence of biochemical ID or ID anemia in exclusively breastfed, partially breastfed, and formula-fed infant were 19%, 6.9%, and 4.8%, respectively. After adjusting for birth weight and prophylactic ferrous sulfate supplementation, breastfeeding was not associated with increased risk of ID or ID anemia.

Conclusion: Incidence of ID at 4-month postnatal age of exclusively breastfed, partially breastfed, and formula-fed preterm infant were not statistically different. Prophylactic iron supplementation at 2 to 4 mg/kg/day should be prescribed to all exclusively or partially breastfed preterm infants of 34 weeks’ gestation or less to prevent ID. The authors recommend checking iron status at the 4-month postnatal time point regardless of feeding type.

Trial registration: Thai Clinical Trials Registry, TCTR20201028002

Keywords: Breastfeeding; Cohort study; Infant iron status; Iron deficiency anemia; Iron supplements; Preterm infants

DOI: doi.org/10.35755/jmedassocthai.2021.06.12800

Received 31 March 2021 | Revised 22 April 2021 | Accepted 28 April 2021