As of 2018, two CAR-T therapies have been approved by the Food and Drug Administration. CAR-T treatment has significant side effects, and loss of the antigen targeted by the CAR-T cells is a common mechanism for relapse. The stem cells that cause different types of leukaemia are also being researched. Leukemia is rarely associated with pregnancy, affecting only about 1 in 10,000 pregnant women. How it is handled depends primarily on the type of leukemia. Nearly all leukemias appearing in pregnant women are acute leukemias. Acute leukemias normally require prompt, aggressive treatment, despite significant risks of pregnancy loss and birth defects, especially if chemotherapy is given during the developmentally sensitive first trimester. Chronic myelogenous leukemia can be treated with relative safety at any time during pregnancy with Interferon-alpha hormones. Treatment for chronic lymphocytic leukemias, which are rare in pregnant women, can often be postponed until after the end of the pregnancy.