The maternal antibodies (IgG) are transferred through the placenta (transplacental transmission) and provide passive immunity to infants during the first months of life, until the first immunizations are administered, or at least until the end of the period when they are most sensitive to the infections covered by vaccines.
The transmission of antibodies through the placenta is a selective, active and intracellular process that starts at the 17th week of pregnancy and progressively increases until the 40th week, when the fetus antibodies reach higher levels than the maternal ones.
