Maternal factors in allergy
Pregnancy presents a paradox for the mother’s immune system because the immune mechanism that protects her from infection also has the potential to destroy her immunologically foreign foetus. Recent studies show that the placenta has a complex function in the regulation of the immune response in both the mother and the foetus during pregnancy. The trophoblast cells of the developing foetus form the interphase between foetal and maternal tissue. The trophoblast possesses specialized immunological features that help to protect the foetus throughout pregnancy. Prominent among the immune protective factors are HLA-G (unique to the placenta) which plays a role in the apoptosis of cytotoxic cells. Moreover, cytokines (particularly IL-4 and IL-10) and hormones (specifically progesterone, prostaglandins) work to suppress Th1 arm and promote Th2 arm of the immune mechanism. (The immune system is broadly divided into Th1-mediated cellular immunity which mobilizes cells to fight virus infection or graft transplants and Th2-mediated humoral immunity that is responsible for the production of antibodies directed against the infecting organism).

The Th1-mediated cytotoxic response of the pregnant mother is suppressed but this compromise promotes the Th2-mediated allergic aspect of the immune response. Thus the baby is born with an allergy-biased immune response which lasts for about 2 years. Maternal exposure to high load of allergenic food or aeroallergens in her environment promotes the appearance of these allergens in the amniotic fluid. If the baby is genetically predisposed to allergy then there is a high risk for the foetus to be subsequently sensitization to the allergens. Hence at birth the baby is ready to react to the allergens if sensitized during foetal development. Recent studies show that maternal avoidance of pollens (e.g. birch tree pollens) during pregnancy reduces the risk of pollen allergy in the fetus. However, restricting the mother’s diet during pregnancy for allergenic foods in general is not recommended. The avoidance of highly allergenic foods (e.g. peanut, bird nest soup, egg, fish, soy, cow's milk) during lactation for the duration of breast feeding is not recommended either. However, if the child on breast milk develops eczema or allergic disease then the food in mother’s diet should be identified through blood allergy tests but the mother should continue to breast feed while avoiding the provoking food.

 

Breast milk has many factors that help to suppress the allergies. However, in atopic mothers supplementation of long chain fatty acids may be necessary since breast milk from atopic mothers has lower levels of essential fatty acids compared to normal breast milk. Mothers should breast feed their babies as long as possible but at least 4 to 6 months. Mothers who are unable to breast feed should consider partially hydrolyzed whey hypoallergenic milk formula (e.g. Nan HA 1 and Nan HA 2) which in several studies has been found to significantly reduce the development of allergies. Weaning with solid foods should be delayed and only low allergic food should be introduced initially. Highly allergenic food should be avoided in early life.