Transfer of IgG subclasses across placenta in term and preterm newborns.

In order to study placental transfer of IgG subclasses, paired blood samples were collected from mothers and umbilical cord of preterm (N = 69) and full-term (N = 68) newborns. The full-term group was further divided into 3 subgroups: appropriate for gestational age (AGA, N = 43), large for gestational age (LGA, N = 13) and small for gestational age (SGA, N = 12), according to birth weight. IgG subclasses (IgG1, IgG2, IgG3 and IgG4) were measured by the single radial immunodiffusion technique using monoclonal antibodies. IgG1 and IgG3 newborn subclass concentrations (10.17 and 0.57 g/l, respectively) increased with increasing gestational age and reached maternal levels (IgG1 = 8.86; IgG3 = 0.67 g/l) during the 37th week of pregnancy. Low levels of these subclasses were found in premature newborns. IgG2 from newborns were always lower than maternal levels (P < 0.05). LGA and SGA newborns had equivalent levels of IgG1 and IgG2 compared with AGA. SGA newborns had higher levels of IgG3 and lower levels of IgG4 than LGA and AGA newborns.