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The accurate identification or prediction of the пїЅhigh-allergic-riskпїЅ newborn is an integral first step in the prevention programme. This needs to occur before, or as soon as possible after, conception in order to allow the mother to practise adequate antenatal prophylaxis in terms of the modification of her own environment. The human foetus is able to produce Immunoglobulin E (IgE) from the 11 th week of gestation. It has furthermore been shown that the unborn foetus is able to mount an intra-uterine allergic response to various allergens which are presumed to have crossed the materno-fetal placental barrier.
Since atopic disease has been shown to be hereditary, the “high-allergic-riskпїЅ newborn may be identified by using the following techniques:
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i. An adequate family history which focuses on the presence or absence of atopic disease in the prospective mother, her husband and her existing children. (i.e. in the first degree relatives of the new born).
ii. The cord blood total polyclonal IgE assay.
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If these measures have not been performed at birth, it is possible to monitor the development of specific IgE antibodies to common ubiquitous allergens during infancy, as possible predictors for subsequent allergic diseases. While not optimal, because of the fact that sensitisation will have already occurred, it is nevertheless of use in some situations
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B. Predictions of the
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пїЅhigh-allergic- riskпїЅ phenotype
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i. Identifying the high-risk Newborn
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1. The atopic family history
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The high-risk pregnancy may be identified by an adequate family history which focuses on the presence or absence of atopy in the prospective mother, her husband, and her existing children. Kjellman (Ref. 1) has laid down clear probability guidelines for the risk of atopic development in offspring who have an atopic family history. These statistics show that the family history of the unborn infant is a good predictor of allergy in its future lifetime, and that the risk of allergic disease for the unborn baby increases with increasing numbers of close relatives with allergy. Table 1 denotes the principles of the family score assessment, recommends which newborns need the cord blood IgE in vitro test at birth, and clarifies which newborns need to embark on the preventative programme during infancy.
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2. Neonatal predictive in vitro tests
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With regard to the identification of the пїЅhigh-allergic-riskпїЅ newborn, the concentration of total serum IgE in newborns has been used as a predictive atopic marker in Caucasoid newborns. These studies have suggested that white newborns in Western First World countries with raised cord blood IgE concentrations are at significant risk of developing future atopy. These neonates are advised to adopt the preventative regimen during infancy. Controversy currently surrounds the exact predictive cut-off threshold level for the cord blood IgE concentration, above which level the newborn is пїЅat riskпїЅ. Values of 0.02 kU/l, 0.5 kU/l and 0.9 kU/l have been proposed.
Recently, there have been reports questioning the predictive value of cord blood IgE determination. Merret et al, Hide et al and Ruiz et al (Ref. 2,3,4) have all found cord blood serum IgE an insensitive predictor for future atopic disease, primarily because of the absence of an accepted and reliable threshold cutt-off value. Nevertheless, the report of Merret and Hide came to these conclusions using пїЅeczemaпїЅ and пїЅwheezingпїЅ as the atopic end-points during infancy.
Studies in Caucasian African newborns, using a combination of a broad range of well defined clinical spectra, and also objective immunological criteria (RAST test positivity during infancy) showed clear differences in the cord blood total IgE concentrations between those infants who become sensitised during infancy, and those who did not. There was not, however, a reliable threshold cut-off level for the cord blood IgE concentrations to differentiate the high-risk newborns, although these studies were not specifically designed to do so. A cut-off level of 0.2 kU/l in First World, Caucasian communities seems to be the most acceptable for practical usage until this issue is resolved.
Other potential cord blood atopic markers, such as anti-bovine milk-specific IgG, total eosinophil counts and platelet counts, have been suggested as additional potential atopic markers. At present the predictive relevance of these atopic markers is being assessed.
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ii Specific preventative initiatives
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With the preceding considerations as the background rationale for the specific preventative measures advocated for the пїЅhigh-allergic-riskпїЅ pregnancy and newborn, the following recommendations currently apply.
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a. Planning the time of conception and birth
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Recent evidence has indicated that babies who are born in the spring, when the pollen season is at its peak, have developed a higher incidence of pollen-related allergic disease than babies born in a season when there is a low environmental count of pollens. It may, therefore, be a worthwhile preventative factor to plan the projected date of conception and the subsequent birth of the infant to avoid the spring pollen season. This may be a particularly important preventative measure in those families who have a family score of 4 or more.
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b. Modification of the pregnant motherпїЅs diet and environment
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Much controversy has surrounded the role of the motherпїЅs diet while she is pregnant, as to the effect of transplacental passage of allergens on the possible causation of allergy in the newborn. Swedish researchers have recently come up with new evidence to show that a motherпїЅs diet while she is pregnant did not influence the pattern of allergic disease in her offspring but other scientists disagree.
In the past, the main principle during pregnancy was to manipulate the diet of the mother so as to prevent allergic foods from making contact with the high-allergic-risk unborn foetus. The current recommendation is for the pregnant mother to ingest whatever balanced diet she feels is recommended for pregnancy in general, but to exclude highly allergenic foods from her diet if possible.
The other important preventative step the pregnant mother should take is to avoid inhaling cigarette smoke. This also means the avoidance of other peopleпїЅs cigarette smoke (passive smoking). Exposure of the foetus to the effects of cigarette by the pregnant mother causes increased levels of IgE in the cord blood of the newborn, and an increased risk of allergy in infancy and childhood.
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