This review examines the risk factors for the development of systemic lupus erythematosus (SLE) flares during pregnancy. In preconception, anti-DNA, hypocomplementemia, previous thrombosis, triple antiphospholipid (aPL) antibody positivity, active lupus nephritis and discontinuation of medications such as hydroxychloroquine and azathioprine are factors associated with pregnancy failure. During pregnancy, SLE flares are associated with aPL antibodies, synergic changes of pregnancy on Th1 and TH2 cytokines, other cytokines and chemokines that interact with hormones such as estrogen and prolactin that amplify the inflammatory effect. From the clinical point of view, SLE activity at pregnancy onset, thrombocytopenia, lupus nephritis, arterial hypertension, aPL syndromes, preeclampsia is associated with lupus flares and fetal complications. In puerperium, the risk factors of flares are similar to pregnancy. Hyperactivity of immune system, autoantibodies, hyperprolactinemia, active lupus nephritis, decrease in TH2 cytokines with increase in TH1 cytokines probably participate in SLE flare. The SLE flares during pregnancy make the difference between an uncomplicated pregnancy and pregnancy with maternal and fetal complications. Therefore, the knowledge of risk factors leads the best treatment strategies to reduce flares and fetal complications in SLE patients.