Urticarial reaction to low molecular weight heparin injections

Low molecular weight heparin (LMWH) is a common agent given in pregnancy; however, cutaneous drug reactions with its use in pregnancy are rarely reported. The case describes a 30-year-old woman with stable Crohn's disease on ustekinumab presenting with a rash at prophylactic LMWH injection sites 30 weeks into her third pregnancy. Skin biopsy reported appearance consistent with an urticarial drug hypersensitivity reaction. A combination of steroid treatment, topical emollient and cessation of LMWH resulted in resolution of symptoms over 2 weeks. Postnatal venous thromboembolism prophylaxis with fondaparinux was uncomplicated. Overall, this case highlights the importance of reporting drug reactions in pregnancy. It additionally exposes a gap in research surrounding immunomodulators and heparins in the development of cutaneous reactions in pregnancy.