The use of low-molecular-weight heparin has been expanded to prevent pregnancy complications such as pregnancy loss, intra-uterine growth restriction and severe early-onset pre-eclampsia in high-risk patients with evidence of acquired or congenital thrombophilia. Therefore, the number of patients with side effects from low-molecular-weight heparin is expected to increase. We describe two women with infiltrating patchy plaques that developed in reaction to low-molecular-weight heparin during pregnancy. In the first patient, a switch to other formulations of heparin and heparinoid failed; the second patient, however, did well when enoxaparin was replaced with dalteparin. This report confirms the risk of skin reactions to enoxaparin and dalteparin, and reports on a skin reaction associated with danaparoid sodium in a pregnant woman.