Immunological tolerance by the mother prevents rejection of the foetus, but aberrations may increase risk of abnormalities like spontaneous abortion, or foetal growth restriction. The neonate is normally colonized with mother's gut microflora, mainly composed of protective anaerobes. This least threatening form of microbial colonization of the neonate, is impaired by sectio delivery, but supported by breastfeeding. Mother's transplacental IgG, secretory IgA and other milk components help protect the neonate together with its own slowly expanding immune system.
Conclusion: The mother's immune system tolerates her foetus via several mechanisms. Failure to do so may cause foetal growth retardation, or spontaneous abortion. The mother and the neonate cooperate in preventing infections in the offspring.