The Immunological Status of the Low Birth Weight (≤ 2100 g) and Very Low Birth Weight (≤ 1200 g) Infant and Relationship to Infection

We prospectively evaluated the immunologic status (IgG, IgM, C3, C4, CH₅₀, and fibronectin) of 45 low (≤ 2100 g) or very low (≤ 1200 g) birth weight infants both during and after hospitalization. Data on infections and illness during the initial hospitalization and 2 to 12 months posthospitalization were obtained. The average nadir IgG, which occurred at 3 months of age, was 66 mg/dl for all infants and 56 mg/dl for very low birth weight (VLBW) infants. Until infants were 5 months of age, IgG was < 200 mg/dl for low birth weight (LBW) infants and < 100 mg/dl for VLBW. IgM increased during the first 7.5 months from an average of 14 mg/dl to an average of 87 mg/dl. The lowest C3 and C4 occurred during the first 3 months. Fibronection did not appear to vary significantly with age. VLBW infants had significantly more (p ≤ 0.002) infections than LBW infants. There was a negative correlation (r = -0.58) between birth weight and the number of hospital infections. There was a significant (p = 0.01) association between an IgG < 50 mg/dl and the number of hospital infections. There were no correlations or associations between infection and the other immunological parameters. The extraordinary low levels of IgG in VLBW infants combined with their prolonged hospitalization involving multiple invasive procedures may play a role in the high frequency of infection seen in this population.