Hypersensitivity Reactions To Low Molecular Weight Heparin In A Pregnant Woman

Itchy, erythematous or eczematous plaques occurring at the site of low molecular weight heparin (LMWH) injection are generally attributed to delayed-type hypersensitivity reactions (DHR) and are reported in the 10% of patients. An even higher risk of reactions to these compounds is described during pregnancy, with an estimated incidence of 19.8%1. Nadroparin is the LMWH with the highest incidence of DHR, as compared, for instance, to dalteparin or enoxaparin. Skin tests, epicutaneous tests and subcutaneous challenge with these compounds have shown an adequate sensitivity and specificity for diagnostic purposes, but we still lack standardised guidelines for selecting safe alternative LMWHs. Cross-reactivity among different LMWHs has been reported in literature in 33-73% of patients. Potential alternative antithrombotic compounds are the heparinoids danaparoid and pentosan polysulfate. Fondaparinux (a chemically synthesised sulfatised pentasaccharide) is actually considered the alternative of choice in cases of allergic reactions to LMWHs, but the experience with this drug during pregnancy is limited to a small cohort of patients, with safety and economical issues yet to be completely addressed. Skin tests with LMWHs have proven to have quite a high negative predictive value, and might be reliably suggested for the identification of safe alternative heparins.