The use of biological therapies for treating autoimmune diseases is increasing. These therapies are sometimes administered to pregnant women as part of a planned therapeutic regimen or to women with unexpected or unplanned pregnancies. The safety of biological therapies in this setting is a major issue. Here, we describe three young pregnant patients with autoimmune disorders: two patients with rheumatoid arthritis and one with idiopathic thrombotic thrombocytopenic purpura. These patients were exposed to rituximab (anti-CD20 monoclonal antibody) or abatacept (fusion protein CTLA4Ig) during the first trimester of their pregnancies. No significant adverse effects or complications were observed during the pregnancies, and all three patients delivered healthy newborns. In the rituximab cases, this result might be explained in part by the very low transplacental maternofetal transfer of rituximab during the first trimester of pregnancy. Despite these favorable outcomes, the use of these two biological agents must follow international recommendations. Their use is not currently allowed during pregnancy except in cases where the potential benefit to the mother justifies the potential risk to the fetus. In the case of exposure to the single agent rituximab during the first trimester, current data suggest that the low risk to the fetus may be outweighed by the potential benefit to the mother.