ABSTRACT
IgG is actively transported across the placenta. Healthy neonates have IgG and IgG subclass values similar to those in their mothers, but have little or no detectable IgM and IgA. Following birth, there is a diminution in the concentration of IgG, reflecting the loss of maternally derived IgG and the gradual accumulation of IgG synthesized by the infant. The physiological low point is normally reached at 3-4 months. In infants born prematurely, the nadir will be proportionately lower, because of the diminished amount of IgG received from the mother and values may remain less than those of term infants throughout the first year after birth. The values in premature infants are lower than those of term infants until 10 months of age. Concentrations of IgM and IgA are also characteristically low at this age, rising gradually thereafter. Quantitative immunoglobulin determination of levels of IgG, IgM, IgA, IgE and IgD (the last not usually performed routinely) may be performed by laser nephelometry, radioimmunoassay or enzyme-linked immunosorbent assays. Levels must be compared with age-matched controls (Table 9.1).11
